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Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics (2011)

Chapter: 9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground

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Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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9
Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground

SUMMARY

Astronomy at radio, millimeter, and submillimeter (RMS) wavelengths is poised for a decade of discoveries. The Atacama Large Millimeter Array (ALMA) will be commissioned in 2013, enabling detailed studies of galaxies, star formation, and planet-forming disks, with spectral coverage from 0.3 to 3 mm, at a resolution approaching 4 milli-arcseconds at the shortest wavelengths. Soon, the Expanded Very Large Array (EVLA) will have an order-of-magnitude more continuum sensitivity than the original Very Large Array (VLA), with continuous spectral coverage from 0.6 to 30 cm. The Herschel Space Observatory, with coverage from 60 to 670 μm, is delivering catalogs of tens of thousands of new “submillimeter-bright” galaxies. The Green Bank Telescope (GBT) operates over a broad range of centimeter and millimeter frequencies and has the potential for vastly improved mapping speeds with heterodyne and large-format bolometric-array cameras. With upgrades, the Very Long Baseline Array (VLBA) will improve astrometric distances critical to studies of star formation, galactic structure, and cosmology. It is possible that gravitational waves will be detected by timing arrays of pulsars, with the Arecibo Observatory playing a crucial role. The University Radio Observatories (UROs) will produce steady streams of excellent science, provide training grounds for graduate students, and remain at the cutting edge of science and technological development. The sizes of detector arrays at millimeter and submillimeter wavelengths and the computational capabilities of digital correlators are both experiencing exponential growth.

The foundation for further advances in this field must be laid in this decade.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

The crucial scientific questions and themes identified today can be addressed if the necessary steps are taken to lead to the instruments of tomorrow. RMS projects of modest cost will provide insights into the origins of the first sources of light that re-ionized the universe and led to the first galaxies. With truly large-format detector arrays on single-dish telescopes, large-scale surveys for galaxies forming stars intensely will inform the origin of the cosmic order observed today. An RMS project will provide insights into fundamental processes on the Sun and use the Sun as a laboratory for understanding the role of magnetic fields in astrophysical plasmas. Upgrades of modest cost to existing RMS facilities may allow the first discovery of gravitational waves and imaging of the event horizon around a black hole. The steps taken during this decade can lead to the next great advance in future decades, a telescope capable of studying the atomic gas flows that fed galaxies back in cosmic time and capable of studying the inner parts of circumstellar disks, where Earth-like planets may be forming. With continued, robust support for studies of the cosmic microwave background (CMB), RMS science extends from the Sun to recombination and the physics of inflation.

The Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground has identified key capabilities that are needed to answer the science questions posed by the five Astro2010 Science Frontiers Panels. By comparing those key capabilities to existing capabilities, the panel identified three new projects for mid-scale funding that will provide critical capabilities. The panel further identified enhancements to existing or imminently available facilities that fulfill other requirements, and this report presents a balanced program with support for small facilities, technology development, laboratory astrophysics, theory, and algorithm development. Priorities and phasing are discussed in the panel report’s final section, “Recommendations.” Those recommendations are summarized here.

Recommended New Facilities for Mid-Scale Funding

The Hydrogen Epoch of Reionization Array (HERA) will provide unique insight into one of the last remaining unknown eras in the history of the universe. The panel recommends continued funding of the two pathfinders (collectively HERA-I) and a review mid-decade to decide whether to build HERA-II. The panel identified specific milestones to be met by HERA-I activities. If those are met, HERA-II is the panel’s top priority in this category of recommended new facilities for mid-scale funding. HERA-I requires about $5 million per year, as is currently being spent, and HERA-II construction is estimated to cost $85 million.

The Frequency-Agile Solar Radiotelescope (FASR) will scan conditions in the chromosphere and corona across the full solar disk once a second, all day, every day. It is a vital complement to the Advanced Technology Solar Telescope (ATST) and provides essential ground truth for studies of magnetic fields on other stars. The

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

estimated construction cost for FASR is $100 million, and operations will cost $4 million per year, both of which the panel assumes will be evenly split between the National Science Foundation’s (NSF’s) Division of Astronomical Sciences (AST) in the Directorate for Mathematical and Physical Sciences and the Division of Atmospheric and Geophysical Sciences (AGS) in NSF’s Directorate for Geosciences.

CCAT (formerly the Cornell-Caltech Atacama Telescope) will provide the capability for rapid surveys of the submillimeter sky, essential for the optimal exploitation of ALMA. CCAT is a 25-m-diameter telescope located on a very high, dry site and equipped with megapixel detector arrays; it will address many of the questions posed by the Science Frontiers Panels. CCAT is estimated to cost $110 million, with $33 million coming from NSF. NSF’s share of operating expenses would be about $7.5 million per year, a net increase of $5 million per year, assuming that current funding for the Caltech Submillimeter Observatory (CSO) is recycled.

FASR and CCAT have equal, and very high, priority in this category, but different phasing.

Development of Current and Imminent Activities

Studies of the CMB have delivered much of the most valuable information about the universe at large. The panel strongly recommends a continued robust program at the current funding levels of ground-based CMB studies, with multiple approaches that are driven by individual investigators.

An expansion of the Allen Telescope Array to 256 antennas (ATA-256) would significantly improve astronomers’ ability to find and study transient sources and to detect gravitational waves by timing an array of pulsars. The ATA can test ideas needed for the development of next-generation telescopes such as the Square Kilometer Array (SKA). The estimated cost of construction for the expansion is about $44 million. The panel recommends that NSF explore collaboration with other agencies and private foundations for the enhancement of ATA-42.

The National Radio Astronomy Observatory (NRAO) telescopes (and soon, ALMA) provide a broad range of scientific capabilities needed to answer many of the SFP questions, but all will need instrument development, especially the completion of frequency coverage, multibeam capability, and electronics improvements to enable much higher data rates. The panel recommends a sustained and substantial program to enhance the NRAO telescopes and ALMA capabilities, amounting to $90 million for NRAO and $30 million for the U.S. share for ALMA over the decade.

The Arecibo telescope is essential for science with pulsars, which test general relativity, constrain the neutron star equation of state, and may lead to the detection of gravitational waves. The telescope can also make the deepest maps of galactic and extragalactic neutral hydrogen currently possible. A future multi-pixel upgrade would dramatically speed up surveys at centimeter wavelengths. The panel

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

recommends that support for Arecibo be enhanced by $2 million per year over projected levels.

The UROs provide cost-effective capabilities, testbeds for technology, and training grounds for young scientists. The panel recommends a modest enhancement ($2 million per year) in the budget for the current program, and it recommends that FASR ($2 million per year, starting in 2015) and CCAT (net $5 million per year, starting in about 2017) be operated under the URO program.

Small Projects

To achieve a balanced program, the panel recommends that a range of small and moderate projects be supported through a combination of funding from the Advanced Technologies and Instrumentation (ATI) program at NSF/AST and from NSF’s Major Research Instrumentation (MRI) program. Examples of such projects include an enhancement of the VLBI’s millimeter-wave capabilities to allow imaging of the event horizon around a black hole and multifeed receivers for the Combined Array for Research in Millimeter-wave Astronomy (CARMA). A program of technology development in a number of areas, and a focused program of laboratory astrophysics, are both vital needs. Support for theoretical work is crucial to realizing the investment in RMS facilities, as is a program of algorithm development. Both will allow observations to confront theory, essential to moving science forward. The panel recommends enhancements to NSF/AST’s ATI program of $1 million per year and an added program of laboratory astrophysics at $2 million per year.

Looking to the Future

The SKA has remarkable discovery potential, including studies of the epoch of reionization (SKA-low), determination of the gas content of galaxies at z of 1 to 2 (SKA-mid), and studies of the terrestrial-planet zones of planet-forming disks (SKA-high). However, substantial technology development is needed to define an affordable instrument. Many areas that the panel recommends for technology development will be crucial for this effort. The HERA project provides a development pathway for SKA-low, and the North American Array (NAA) project (part of NRAO development) develops technology for SKA-high. The panel recommends the continued development and exploration of options for realizing SKA-mid.

THE SCIENCE CASE

Here the panel identifies the RMS capabilities (in italic) that are needed to answer the science questions raised by the Science Frontiers Panels (SFPs) and summarizes them (as numbered below) in Table 9.1 at the end of this section and

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

also maps them in Figure 9.6 there. The panel lists only the SFP questions that RMS facilities can address. It also poses some additional, unnumbered, relevant questions. In later sections, the panel matches these capabilities to specific activities and concludes with recommendations.

Cosmology and Fundamental Physics (CFP)

Q1: How did the universe begin? The CFP report requires a suite of instruments that characterize the cosmic microwave background (CMB) to determine properties of the early universe. CMB observations probe the potential-energy function of the primordial field (or fields), the type of primordial fluctuation (adiabatic or iso-curvature), whether the fluctuations were Gaussian, and the degree to which gravitational waves (tensors) played a role in the infant universe. CMB observations may yield the only observational constraint on theories of quantum gravity. These measurements will complement the Planck satellite, which will have exquisite sensitivity to temperature fluctuations for 2 < l < 2,500, where l is the multi-pole index of a spherical harmonic; the corresponding angular scale is θ ~ 180/l in degrees. With new CMB polarization measurements in the range 2 < l < 200, one can find or limit primordial gravitational waves and probe reionization. The polarization for 200 < l < 3,500 sheds light on early-universe physics, neutrino mass, and the helium abundance. The temperature spectrum for 1,000 < l < 10,000 should be pursued from the ground to understand the high-l tail of the primary CMB spectrum and, for example, to identify clusters through the Sunyaev-Zel’dovich effect (SZE). The search for large-angular-scale B-modes (from tensor fluctuations) will discover them or decrease the current limit on the tensor-to-scalar ratio from about 0.3 to 0.01. These techniques lay the foundation for a future satellite focusing on polarization.


Q2: Why is the universe accelerating? It is known that the universe is accelerating but not why or how. To make progress, the z-dependence of the dark-energy equation of state, w(z), and the Hubble parameter, h(z), must be better determined. Intimately related to these are possible changes in the gravitational coupling constant (G) and the growth rate of structure. The CFP report calls for precision tests of general relativity, which is central to our understanding of cosmology. Studies of pulsars in relativistic binary systems provide the strongest constraints on possible changes in G, and timing may allow detection of gravitational radiation from the early universe. Our capabilities to find relativistic binary pulsars and time them must be enhanced. Additional tests will come with measurements of the supermassive black hole (SMBH) in the center of our galaxy with ultrahigh spatial resolution and through gravitational lensing of radio by SMBHs in distant galaxies, requiring sensitive centimeter-wave imaging. The growth of structure will be measured a

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

number of ways with the CMB. Through the SZE, measurements of clusters can provide a mass-selected, almost z-independent sample of clusters of galaxies over large regions of sky, tracing the development of clusters from the early to nearby universe.


Q4: What are the properties of neutrinos? The presence of relativistic neutrinos affects the growth of structure at early times. High-l CMB-lensing B-modes are particularly sensitive to this effect, as are other aspects of the measurements. CMB experiments are expected to determine the sum of neutrino masses to 0.05 eV. A vigorous ground-based CMB program is a requirement in this area.


Discovery area: Gravitational wave astronomy—listening to the universe. The CFP report calls for pulsar timing arrays to probe the nanohertz frequency range to detect the stochastic background of gravitational waves from SMBH binaries (Figure 9.1). A project focusing on this goal is discussed in the PAG report, and so only the consequences for RMS facilities are summarized here. A rough requirement for gravitational-wave detection is careful timing of the arrival of pulses from a set of ~20 stable, millisecond pulsars distributed over the sky to an accuracy of 100 ns over a period of 5 years. This task may be divided into two parts: discovery and timing. Discovery requires large collecting area, wide bandwidths, high-throughput back-end electronics, and computational power. In the United States, pulsar-discovery capabilities exist primarily at Arecibo and the GBT. They must be sustained and upgraded. Timing requires about a day per week of observations by a telescope with 104 m2 collecting area and with back-end hardware and software capable of coherent dispersion removal. Observations across a wide bandwidth or at multiple simultaneous frequencies are essential to correct for effects due to interstellar dispersion. Timing requires either the reallocation of existing facilities or ideally a facility with a large fraction of the time dedicated to timing.

Galaxies Across Cosmic Time (GCT)

Enabled in part by RMS observations with new facilities and instrument technologies, an understanding of the formation and evolution of galaxies and large-scale structure is beginning to form. However, fundamental questions remain. The observed structures of galactic dark-matter halos challenge structure-formation theories. The interaction of gas and stars in the galaxy-building process is poorly understood, driving a need for inventories of the cold atomic and molecular gas contents of galaxies. Supermassive black-hole growth and feedback must be characterized to understand the correlation between black-hole masses and stellar-bulge velocity dispersions. At the highest redshifts, the nature of the first objects that reionized the universe remains unconstrained.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×
FIGURE 9.1 Black holes orbiting one another produce ripples in space-time or gravitational waves. Left: The ripples from a single supermassive black-hole binary cause the signals traveling from two pulsars to the telescope to arrive faster or slower than expected if they were traveling through flat space. Right: The superposition of many supermassive black-hole binaries distributed throughout the universe gives rise to a low-frequency stochastic background. This background will induce correlated shifts in the arrival times of an array of pulsars. SOURCE: Left: D. Backer/JPL/NASA. Right: David Champion, Max-Planck-Institut für Radioastronomie.

FIGURE 9.1 Black holes orbiting one another produce ripples in space-time or gravitational waves. Left: The ripples from a single supermassive black-hole binary cause the signals traveling from two pulsars to the telescope to arrive faster or slower than expected if they were traveling through flat space. Right: The superposition of many supermassive black-hole binaries distributed throughout the universe gives rise to a low-frequency stochastic background. This background will induce correlated shifts in the arrival times of an array of pulsars. SOURCE: Left: D. Backer/JPL/NASA. Right: David Champion, Max-Planck-Institut für Radioastronomie.

Q1: How do cosmic structures form and evolve? RMS facilities can characterize the shapes and substructures of galactic halos using high-angular-resolution observations of gravitational lensing. The EVLA will find hundreds of lenses, but ultimately approximately 106 lenses will be needed, requiring a capability for very sensitive centimeter-wave imaging. Unbiased by redshift, SZE surveys associated with the CMB program will discover large samples of clusters out to their epoch of formation. Understanding the physics of these clusters will require multiwavelength observations, including detailed centimeter and millimeter observations (Figure 9.2).


Q2: How do baryons cycle into and out of galaxies, and what do they do while they are there? A comprehensive model of galaxy formation requires an understanding of accretion, mergers, and evolution of the gas in galaxies from the formation of the first galaxies to the present day. For studies of dusty, distant, star-forming galaxies, large-area (tens of square degrees), continuum submillimeter surveys will sample the galaxy luminosity function over a broad range of redshifts. Large, single-dish submillimeter and millimeter telescopes equipped with large-format detector arrays are needed. To characterize the gas associated with star formation, spectroscopy of CI, CO, and molecular tracers of dense gas is essential. The current ALMA and EVLA facilities will offer broad but incomplete coverage in redshift for the detection of CO in distant galaxies. New facilities and upgrades can enable fast

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×
FIGURE 9.2 Deep submillimeter extragalactic image in the GOODS-N region obtained with the Hershel Space Observatory SPIRE camera. The three images at the left are in three bands, which are coded in those colors in the large composite. All the sources are dusty galaxies. Bluer galaxies are warmer and/or more nearby, while redder galaxies are cooler and/or at higher redshift. The submillimeter sky is extremely rich in galaxies—thousands of (unresolved) high-redshift galaxies appear, and the image is highly confusion-limited. SOURCE: Courtesy of the European Space Agency and the SPIRE and HerMES consortia.

FIGURE 9.2 Deep submillimeter extragalactic image in the GOODS-N region obtained with the Hershel Space Observatory SPIRE camera. The three images at the left are in three bands, which are coded in those colors in the large composite. All the sources are dusty galaxies. Bluer galaxies are warmer and/or more nearby, while redder galaxies are cooler and/or at higher redshift. The submillimeter sky is extremely rich in galaxies—thousands of (unresolved) high-redshift galaxies appear, and the image is highly confusion-limited. SOURCE: Courtesy of the European Space Agency and the SPIRE and HerMES consortia.

spectroscopic follow-up observations of galaxies detected in continuum surveys, particularly in the z = 2 to 4 range. This goal requires complete submillimeter-millimeter frequency coverage, broadband correlators, and multiobject spectroscopic capability for single-dish telescopes. Large-scale intergalactic gas flows and early accretion onto galaxies will consist largely of atomic hydrogen. H I 21-cm line observations can assess the total masses and atomic gas contents of galaxies, circumgalactic streams, and the cosmic web, mapping the gaseous origins of galaxies. The current suite of centimeter-wave telescopes are limited to observing H I structures in the local (z < 0.2) universe. Detecting H I in galaxies at redshifts as high as z ~ 1 will require very sensitive centimeter-wave imaging, requiring a

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

large increase in collecting area over current facilities and substantially increased correlator capabilities.


Q3: How do black holes grow, radiate, and influence their surroundings? Supermassive black holes are ubiquitous in the centers of galaxies. However, much still needs to be learned about how they become active galactic nuclei (AGN), and how they interact with their host galaxies. Ultrahigh-spatial-resolution interferometric observations can resolve regions close to AGN: jet-formation mechanisms can be constrained by VLBA and submillimeter VLBI observations of blazars, and submillimeter VLBI will enable studies of circumnuclear disks in galaxies, including our own.


Q4: What were the first objects to light up the universe, and when did they do it? The epoch of reionization (EoR) is the frontier in understanding galaxy formation. Understanding cosmic reionization at z > 6 requires mapping the H I distribution via the hyperfine transition, which is redshifted to meter-wavelengths for z > 5. The first-generation instruments (PAPER, MWA, EDGES, and international efforts) are designed to detect fluctuations and constrain the redshift range of reionization. Precise measurement of the power spectrum of H I emission requires a sensitive meter-wave array with a factor-of-10 larger collecting area (Aeff ~ 105 m2). Imaging hydrogen structures will require another order of magnitude in collecting area (Aeff ~ 106 m2). Whether stars in galaxies or other sources are primarily responsible for cosmic reionization remains controversial. The roughly constant apparent brightness of dusty galaxies of a given luminosity as a function of redshift in submillimeter and millimeter bands provides an advantage for fast surveys at millimeter/submillimeter wavelengths. Observations of redshifted CO, C II, N II, and O I have the potential to measure the radiative cooling of galaxies in the later stages of the EoR, requiring complete wavelength coverage in spectral windows accessible from the ground.

The Galactic Neighborhood (GAN)

The galactic neighborhood (GAN) science frontier covers galaxy build-up and evolution back to z ~ 0.1. RMS facilities are well suited for GAN studies through their ability to probe cold flows, star formation, the environment of SgrA*, and magnetic fields. RMS interferometers provide high resolution and high astrometric accuracy (Figure 9.3).


Q1: What are the flows of matter and energy in the circumgalactic medium? Nearly all massive galaxies are accreting material, observed as H I and stellar streamers from tidally disrupted satellite galaxies. Radio facilities are required to assess the kinematics and distributions of H I on both large (low-resolution) and small (high-

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×
FIGURE 9.3 Neutral hydrogen (H I) gas in the Virgo cluster of galaxies taken with the VLA, colored by velocity (galaxy sizes have been increased by a factor of 10 to make them more visible). The background image is from ROSAT. SOURCE: NRAO/AUI and Chung et al., Columbia University.

FIGURE 9.3 Neutral hydrogen (H I) gas in the Virgo cluster of galaxies taken with the VLA, colored by velocity (galaxy sizes have been increased by a factor of 10 to make them more visible). The background image is from ROSAT. SOURCE: NRAO/AUI and Chung et al., Columbia University.

resolution) scales. Feedback in galaxies from star formation or AGN activity may enhance or halt additional star formation. By imaging radio synchrotron emission, H I, and molecular lines, one can assess the impact of feedback on the surrounding medium. Sensitive, low-resolution observations with radio facilities play a crucial role in studying feedback on large scales, but efficient, high-resolution, centimeter-wave capabilities are needed to provide maps of energy deposition into the ISM.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

Q2: What controls the mass-energy-chemical cycles within galaxies? RMS facilities play a critical role in studying the build-up of stellar mass by gas inflow and accretion over cosmic time. H I is a prime tracer of the inflow of gas into galaxies, some of which becomes star-forming H2 clouds. Observations of dust emission and molecular lines (millimeter-submillimeter) trace the gas, and synchrotron emission from supernovae traces star-formation rates. Very sensitive 2-cm imaging and fast surveys at submillimeter wavelengths and full wavelength coverage from meter to submillimeter will be required to achieve the goals.


Q4: What are the connections between dark and luminous matter? The H I disks of galaxies extend well beyond the stellar light of galaxies and were instrumental in providing evidence of dark matter. Sensitive, high-resolution H I observations are required to trace the kinematics of the faint, dark-matter-rich dwarf galaxies and the outer parts of disk galaxies. Accurate measurements of the properties of SMBHs and their interplay with their immediate gaseous environments are required to understand how SMBHs fit into the build-up and evolution of galaxies, including nuclear star-forming rings. These science goals require high-resolution (<0.05 ″) radio and millimeter observations to probe the non-thermal emission and state of the star-forming gas, respectively. Ultrahigh resolution at millimeter/submillimeter wavelengths tantalizes us with the possibility of imaging the event horizon of Sgr A*.


Discovery area: time-domain astronomy. Temporal RMS observations are a largely unexplored area of astronomy likely to show significant progress in the next decade. Such observations require a sensitive, dedicated instrument designed to scan the available sky rapidly enough to sample variable (or moving) objects. A dedicated transient-search telescope covering a wide range of wavelengths is needed to explore this discovery space.


Discovery area: astrometry. One of the great strengths of RMS interferometers is the direct detection of electromagnetic phase and the ability to do astrometry routinely to a fraction of a beamwidth. Parallaxes and proper motions can be measured within the galaxy, and for galaxies within the Local Group and beyond, allowing for a better assessment of dynamics and everything that comes with better distances. An ultrahigh-resolution capability with improved sensitivity is needed for precision astrometry.

Stars and Stellar Evolution (SSE)

Q1: How do rotation and magnetic fields affect stars? For many years, radio observations have provided clues to magnetically driven solar and stellar activity. In

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

the next decade, they have the potential to do much more. New data on magnetic fields in the Sun’s corona and chromosphere can help characterize how magnetism powers stellar atmospheres. Spatially resolved, high-time-cadence broadband imaging spectroscopy is required to obtain vector magnetic field measurements and to detect sites of magnetic reconnection and particle acceleration. Full-Sun, continuous observations are also needed both to map the global magnetic field and to survey magnetically driven dynamics. Such observations, in conjunction with the full range of multiwavelength observations of chromospheric and coronal plasma, together with three-dimensional models and laboratory analyses of magnetic reconnection, can synthesize an understanding of solar magnetism (Figure 9.4). That understanding can be extended outward to stars and throughout plasma astrophysics. A dedicated solar radio telescope is needed for this synthesis.

FIGURE 9.4 Models for magnetic fields on the Sun. SOURCE: Jeongwoo Lee, New Jersey Institute of Technology.

FIGURE 9.4 Models for magnetic fields on the Sun. SOURCE: Jeongwoo Lee, New Jersey Institute of Technology.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

Q2: What are the progenitors of Type Ia supernovae and how do they explode? Radio observations are important probes into the origins of exploding stars, such as Type Ia supernovae (SNe). In particular, radio emission arises from circumstellar material disturbed by the explosion. Therefore, sensitive and rapid follow-up radio detections of Type Ia SNe with flexible radio interferometers can provide crucial insight as to the progenitor phase of these SNe.


Q3: How do the lives of massive stars end? Episodes of extreme mass loss preceding the deaths of massive stars can hide the explosions from observations at shorter wavelengths, but they can be traced in the radio with sensitive interferometric observations, spaced at appropriate intervals. Radio and X-ray observations can also be combined to trace the shock physics occurring when these massive ejecta propagate into the interstellar medium. Such a synthesis of radio and X-ray observations requires high spatial resolution in the radio (at least ~1″), comparable to Chandra. “Orphan afterglows” of gamma-ray bursts are best studied in the radio using dedicated transient survey instruments.


Q4: What controls the mass, radius, and spin of compact stellar remnants? Nearly 2,000 neutron stars are known today, the majority of which have been discovered and characterized through radio observations. The measurement of relativistic effects through binary pulsar timing yields accurate neutron-star and (likely compact-object) companion masses. Relativistic spin-orbit coupling should be detectable for the double-pulsar system within the next decade and will yield the neutron-star moment of inertia, providing an important constraint on the equation of state. Pulsar searches with excellent short-period sensitivity will determine whether gravitational-wave damping is important for limiting minimum spin periods. The spin of a black hole could be determined through the detection of relativistic spin-orbit coupling in a pulsar/black-hole binary. Large-scale surveys, with short-period sensitivity, and search algorithms that correct for binary acceleration are necessary to discover these systems. Frequent and long-term timing of these discoveries will then be needed to yield fundamental constraints on the equation of state. Surveys with large telescopes and the ability to time multiple pulsars simultaneously and commensally with other surveys are necessary.


Discovery area: time-domain astronomy. The next decade promises discoveries of both new source classes and new phenomena from known sources. Transient radio emission is expected from the Sun, flaring stars, neutron stars, tidal disruptions, local and cosmological supernovae, gamma-ray bursts, and, possibly, extraterrestrial civilizations. Radio observations probe energetic and/or explosive processes associated with high magnetic fields and provide unique information not available at other wavelengths. To fully exploit the expected parameter space, large-field-of-

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

view surveys with time resolutions of a millisecond or less are required. Optimally, the same region of sky would be surveyed multiple times. New facilities must also enable prompt radio follow-up of sources found at other energies. Effective monitoring of solar transients also requires a field of view sufficient to image the entire Sun.

Planetary Systems and Star Formation (PSF)

Q1: How do stars form? With transformative new RMS instruments coming on line early in the next decade, and key missing capabilities under development, we are poised to address fundamental questions about how, where, and under what physical conditions stars form across the whole spectrum of the stellar mass function. The capabilities required are a combination of fast-survey capabilities at millimeter/submillimeter wavelengths and fast, sensitive surveys at centimeter wavelengths to conduct wide-field surveys at 5- to 20-arcsecond resolution, coupled with more sensitive, sub-arcsecond resolution follow-up of selected regions. Accurate distances obtained via ultrahigh-resolution capability are fundamental.


What determines star-formation rates and efficiencies in molecular clouds? In the solar neighborhood, typically only a few percent of the mass of a giant molecular cloud (GMC) is converted into stars. Understanding what controls star-formation rates and efficiencies in clouds in our galaxy can inform models of galaxy evolution (Figure 9.5). Large-area surveys of GMCs and their deeply embedded star-forming regions require fast millimeter/submillimeter surveys. Diagnostics of the physical properties of star-forming regions require spectroscopy of molecular and ionized gas, as well as observations of dust, free-free emission, non-thermal continuum emission, and polarization on spatial scales ranging from 0.1 to 100 pc, corresponding to 0.05 to 200 arcseconds, to extend the study to nearby galaxies at ~10 Mpc.


What determines the properties of pre-stellar cloud cores, and what is the origin of the stellar mass function? Stars form in dense cores of size ~0.1 pc. Similarities between the core mass function (CMF) and the mass distribution of stars (stellar IMF) raise the question, Is the CMF, and potentially the stellar IMF, dependent on environment? Studies of more distant regions, with comparable spatial resolution, are needed. Exploration of the CMF is limited by current sensitivity and angular resolution, as well as by uncertainties in the dust emissivity and temperature. Dramatic progress can be made with sensitive, high-angular-resolution, multiwavelength spectral-line and dust-continuum data, from the centimeter to far-infrared, on 0.01-pc scales, requiring a best resolution of 0.05 arcseconds (to access the LMC and SMC). Fast-survey capability at submillimeter wavelengths is needed to assemble complete samples.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.5 Model of the Milky Way with star-forming regions indicated; before recent VLBA measurements, these regions did not align with spiral arms. SOURCE: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF.

FIGURE 9.5 Model of the Milky Way with star-forming regions indicated; before recent VLBA measurements, these regions did not align with spiral arms. SOURCE: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF.

Q2: How do circumstellar disks evolve and form planetary systems? Circumstellar disks are ubiquitous by-products of low-mass star formation, an inevitable consequence of angular-momentum conservation and gravitational collapse. A suite of panchromatic observations has been used to characterize the bulk properties of the disks around pre-main-sequence stars, establishing them as potential sites for planet formation. Both ALMA and a large, single-dish, millimeter/submillimeter telescope play key roles because these disks are impenetrable at shorter wavelengths. A complete understanding of the origins and diversity of planetary systems will require multiwavelength observations of large samples of disks to probe their structure, to discover features associated with planets, and to identify evolutionary trends.


What is the nature of the planet-forming environment? How do giant planets accrete from disks, and what are these young planets like? While current RMS facilities offer a glimpse of disk structure on scales >20 AU, imminently available new facilities are poised to resolve dust and gas tracers on scales down to 1 AU with high fidelity. Such revolutionary observations have the potential to directly reveal spiral density waves, accretion streams, snow lines, and regions prone to rapid gravitational instabilities. A new frontier will be the inner-disk regions of terrestrial-planet formation at milli-arcsecond scales, where low dust opacities are reached only at long millimeter and short centimeter wavelengths. Imaging these small regions will require the development of very sensitive centimeter-wave telescopes with excellent resolution.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

What can debris disks and the Kuiper belt reveal about the dynamical evolution of planetary systems? Imaging- and modeling-resolved features in debris disks—such as central cavities, offsets, and clumps—(and their proper motions) can locate unseen planets, particularly at separations >10 AU, where classical indirect planet-detection techniques become difficult. The debris features may encode a historical record of the system dynamics, similar to the scattered and resonant populations of the Kuiper belt. Large-format bolometer arrays on single-dish telescopes at millimeter/submillimeter wavelengths will be required to assess both the full range of debris-disk properties—as well as the frequency of large-separation planets—and the habitability of terrestrial planets in the heavy bombardment phases that create debris disks.


Q4: Do habitable worlds exist around other stars, and can we identify the telltale signs of life on an exoplanet? The ultimate question is whether humans are alone. Discovery of potentially habitable worlds is imminent, and the PSF report explores the options for finding “telltale” signs of life on exoplanets. Of course, the most certain sign of extraterrestrial life would be a signal indicative of intelligence. An RMS facility that devoted some time to the search for extraterrestrial intelligence would provide a valuable complement to the efforts suggested by the PSF report on this question. Detecting such a signal is certainly a long shot, but it may prove to be the only definitive evidence for extraterrestrial life.

Summary of Needed Capabilities

The panel collected in Table 9.1 and illustrated in Figure 9.6 the RMS capabilities noted in the previous discussion and identified the SFP questions for which they are most crucial. These capabilities will impact many other questions besides those noted here.

THE PROGRAMMATIC CONTEXT

The RMS region covers more than five decades in wavelength, from the boundary of the far-infrared, at λ = 200 μm, to the ionospheric cutoff, λ = 30 m. Table 9.2 lists the RMS facilities open to U.S. investigators—either currently operating or under construction—excluding dedicated experiments, such as CMB or EoR experiments. Below the panel summarizes their capabilities, noting links to SFP questions and needed capabilities (see Table 9.1).

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

TABLE 9.1 Capabilities Needed to Address RMS-Related Science Questions Identified by the Astro2010 Science Frontiers Panels

Capability

CFP

GCT

GAN

SSE

PSF

Cosmic microwave background program

Q1, 2, 4

Q1

 

 

 

Sensitive meter-wave array

 

Q4

 

 

 

Solar radio telescope

 

 

 

Q1, Discovery

 

Fast millimeter/submillimeter surveys

 

Q2, Q4

Q2

 

Q1, 2

Fast centimeter surveys

 

 

Q2

Discovery

Q1

Efficient high-resolution imaging at centimeter/millimeter

Q2

Q2

Q1, Q4

Q3

Q1, 2

Very sensitive centimeter imaging

 

Q1, 2

 

 

 

Dedicated pulsar timing, transients

Q2, Discovery

 

Discovery

Q2, 3, 4, Discovery

Q4

Ultrahigh resolution

Q2

Q3

Q4, Discovery

 

Q1

Complete wavelength coverage

 

Q2, 4

 

 

 

FIGURE 9.6 Mapping of Astro2010 Science Frontiers Panel areas to needed radio, millimeter, and submillimeter capabilities.

FIGURE 9.6 Mapping of Astro2010 Science Frontiers Panel areas to needed radio, millimeter, and submillimeter capabilities.

Status of Current U.S. National RMS Facilities

National RMS facilities are funded primarily by NSF-AST (Table 9.2). They may be used on an equal basis by the entire international astronomical community under an “open skies” policy. The National Radio Astronomy Observatory operates a number of telescopes under the management of Associated Universities, Inc.,

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

TABLE 9.2 U.S. Radio Astronomy Facilities

Observatory

Telescope

Wavelength (cm)

Aperture

Collecting Area (sq m)

Angular Resolution

Field of View

Commissioned

Source of Funding

Existing

NRAO

Very Large Array (VLA)

0.7-400

27 × 25 m

13,250

1″–44″ (λ/21 cm)

30′ (λ/21 cm)

1982

NSF, Mexico, Canada

NRAO

Expanded Very Large Array (EVLA)

0.7-21

27 × 25 m

13,250

1″–44″ (λ/21 cm)

30′ (λ/21 m)

2012

NSF

NRAO

Very Long Baseline Array (VLBA)

0.3-90

10 × 25 m

4,900

0.005″ (λ/21 cm)

30′ (λ/21 m)

1993

NSF

NRAO

Green Bank Telescope (GBT)

0.3-100

100 m

7,850

9′ (λ/21 cm)

9′ (λ/21 cm)

2000

NSF

NAIC

Arecibo Observatory

3-100

225 m

40,000

3′ (λ/21 cm)

3′ (λ/21 cm)

1963

NSF

Hat Creek Radio Observatory

Allen Telescope Array (ATA)

3-60

42 × 6 m

1,200

4′ × 2′ (λ/21 cm)

2.5° (λ/21 cm)

2007

Berkeley, USAF, DARPA, private, NSF

CARMA

Combined Array for Research in Millimeter-wave Astronomy (CARMA)

0.1-0.3

6 × 10 m, 9 × 6 m, 8 × 3.5 m

850

0.2″–4″ (λ/1.3 mm)

44″ (λ/1.3 mm)

2007

NSF, Caltech, Berkeley, Illinois, Maryland

Caltech Submillimeter Observatory

Caltech Submillimeter Observatory (CSO)

0.13-0.035

10.4 m

85

25″ (λ/870 mm)

25″ (λ/870 mm)

1988

NSF, Caltech, Texas

Arizona Radio Observatory

12-Meter Telescope

0.3-0.13

12 m

110

55″ (λ/3 mm)

55″ (λ/3 mm)

1985

Arizona

Arizona Radio Observatory

Submillimeter Telescope

0.13-0.035

10 m

78

25″ (λ/870 mm)

25″ (λ/870 mm)

1993

Arizona

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

CARA

South Pole Telescope (SPT)

0.1-0.3

10 m

78

42″ (λ/1.5 mm)

42″ (λ/1.5 mm)

2007

NSF

SAO/ASIAA

Submillimeter Array (SMA)

0.035-0.2

8 × 6 m

226

0.3″-3″ (λ/870 mm)

30″ (λ/870 mm)

2003

Smithsonian/ASIAA

Under Construction

INAOE/University of Massachusetts

Large Millimeter Telescope (LMT)

0.13-0.3

50 m

1,960

12″ (λ/3 mm)

12″ (λ/3 mm)

2010+

INAOE and University of Massachusetts

Long Wavelength Array

Long Wavelength Array (LWA)

300-3,000

256 dipoles

2″ (λ/1.5 m)

8° (λ/1.5 m)

2012+

University of New Mexico, NRL, LANL, Virginia Tech, NRAO, USAF, University of Iowa

NRAO

Atacama Large Millimeter/submillimeter Array (ALMA)

0.3-0.035

50 × 12 m

5,700

0.02″ (λ/1 mm)

15″ (λ/870 mm)

2013

NSF, Canada, ESO, Japan, Chile

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

with NSF support. NASA occasionally contributes to ground-based RMS facilities for mission-oriented purposes—as, for example, in the NASA-funded upgrade of the VLA that enabled it to join the Deep Space Network to receive transmissions from Voyager 2 at Neptune. The panel lists the national facilities below in order of decreasing age since commissioning.

Arecibo Observatory

The 305-m Arecibo Telescope is a facility of the National Astronomy and Ionosphere Center (NAIC), currently operated by Cornell University under cooperative agreement with NSF. Arecibo is the largest telescope in the world. It is equipped with a 7-element 21-cm array (ALFA) and participates in VLBI. Arecibo is the most sensitive H I telescope, and feasibility studies have begun on a 40-beam survey array for H I surveys of the nearby universe (GAN 1, 2; GCT 2). Arecibo is the most sensitive telescope for pulsar astronomy. Discovery of millisecond pulsars is critical to the pulsar-timing-array effort (CFP Discovery). Arecibo radar, with the NASA Goldstone antenna, is critical to the characterization of potentially catastrophic incoming near-Earth objects (NEOs), the subject of the recent NRC study, Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies.1

Very Large Array (VLA)

Dedicated in 1980, the NRAO VLA is a centimeter-wave array of 27 25-m dishes, with four configurations corresponding to maximum baselines of 1 to 36 km. A nearby VLBA antenna can be added to give a best angular resolution of 0.04″. The VLA has been a productive instrument, yielding 170 refereed papers per year since the mid-1980s. It is in the process of a major equipment upgrade, the “Expanded VLA,” described below.

Very Long Baseline Array (VLBA)

The NRAO VLBA consists of 10 25-m dishes, spread over baselines up to 8,000 km, allowing centimeter-wave imaging at resolutions to 80 micro-arcseconds and astrometry to 10 micro-arcseconds. The VLBA has major scientific impact in science areas that require high astrometric accuracy, such as parallaxes and proper motions. The VLBA has been used to study the proper motions of Sgr A* and

1

National Research Council, Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies, The National Academies Press, Washington, D.C., 2010.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

nearby galaxies (GAN Discovery), Keplerian maser disks and black-hole masses in nearby galaxies (GCT 3; GAN 4), precision parallaxes for star-forming regions in the Milky Way, and superluminal motions in AGN jets (GCT 3). Upgrading of receivers and bandwidth is essential to improve the sensitivity of this ultrahigh-resolution capability.

Robert C. Byrd Green Bank Telescope (GBT)

The Robert C. Byrd Green Bank Telescope of the NRAO is a 100-m dish operating from 3 mm to 1 m. Dedicated in 2000, it is the largest fully steerable telescope in the world. In addition to heterodyne receivers, the GBT has the 3-mm bolometer array MUSTANG. The GBT is an efficient millisecond-pulsar machine and a sensitive instrument for mapping H I and recombination lines. It can detect CO and HCN emission from high-redshift galaxies (GCT 2). MUSTANG is being used to study the SZE toward massive clusters (GCT 1). With upgrades (S4.3), the GBT can provide much of the needed capability for fast centimeter-wave surveys (PSF 1, 2).

Current U.S. University Radio Facilities

University radio facilities are an integral part of the U.S. RMS capabilities. Those receiving NSF/AST operations funding are part of the URO program, and the fraction of their observing time funded by NSF is subject to an “open skies” policy. Capital funding for construction of university telescopes is a mix of NSF money and alternative sources such as endowments, gifts, and state funding. Since the closure of the NRAO 12-Meter Telescope in 2000, there has been no national U.S. facility in the millimeter and submillimeter portion of the spectrum. U.S. access for observing at these wavelengths has been provided exclusively by the university facilities, which have also made major contributions to the technological developments leading to ALMA. The panel discusses below the facilities that currently receive operations support from the URO program, and then those currently without URO funding.

Caltech Submillimeter Observatory (CSO)

The CSO operates a 10.4-m telescope on Mauna Kea with an active surface. It can be used as an element of the Submillimeter Array, along with the JCMT. Since 1984, the CSO has pioneered the development of submillimeter heterodyne receivers. Continuum cameras include Bolocam, operating at λ = 1.1 and 2.1 mm, and SHARC II, at λ = 350 and 450 μm. Science from the CSO is wide-ranging:

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

atmospheric chemistry of Earth and other planets, comet chemistry, turbulence in molecular clouds, CO and CI lines in other galaxies, magnetic-field mapping of star-forming clouds, interstellar-cloud chemistry (GAN 2), and the SZE (GCT 1). The CSO has recently completed a 1-mm continuum survey of the galactic plane with Bolocam (PSF 1). These areas of research can now be followed up using ALMA. The CSO will be decommissioned in 2016.

Combined Array for Research in Millimeter-wave Astronomy (CARMA)

The Berkeley-Illinois-Maryland Association Array and the Owens Valley Millimeter Array were merged to form CARMA in 2003, a joint effort of the California Institute of Technology, the University of California, Berkeley, the University of Illinois, and the University of Maryland. The SZE array of the University of Chicago has recently been added. CARMA was a recommendation of Astronomy and Astrophysics in the New Millennium (AANM), the 2001 decadal survey report. CARMA consists of six 10.4-m, nine 6.1-m, and eight 3.5-m antennas at a high site, providing arcsecond imaging in the 3-mm and 1-mm atmospheric windows. CARMA images molecular line emission from comets, star-forming regions, nearby and distant galaxies, and the SZE. CARMA can be used for VLBI, including recent observation of Sgr A* at 1 mm (GAN 4; GCT 3). CARMA is just beginning to operate at full capacity. Operations are funded in part by NSF, and as a result, 30 percent of the observing time is “open skies.” Upgrades to CARMA (S4.4) can test multi-beam systems on interferometers and enhance survey capability (see Table 9.1).

Allen Telescope Array (ATA-42)

The ATA consists of 42 6-m antennas acting together as a fast, wide-field, centimeter-wave mapper, a joint project of the SETI Institute and the University of California, Berkeley. High resolution and a large field of view make the ATA an excellent instrument for mapping degree-scale H I structures such as tidal tails in the local universe (GAN 1, 2). The ATA currently devotes part of its observing time to the search for radio transients over wide fields of view (GAN Discovery; SSE Discovery), and it carries out SETI monitoring (PSF 4) simultaneously with other observing. Technology under development at the ATA, such as large-N correlators, beam-forming techniques, commensal observing strategies, and data management, will influence directions taken in future centimeter-wave arrays, such as the SKA. Construction of the first 42 antennas was funded by Paul Allen. The operations budget is funded modestly by NSF ($200,000 annually) and the state of California, and through partnerships with the USAF and the USNO. These arrangements limit the time available for astronomy.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×
Arizona Radio Observatory (ARO)

The ARO comprises two telescopes in Arizona run by Steward Observatory, the 12-m telescope (formerly operated by NRAO) on Kitt Peak, and the 10-m Submillimeter Telescope on Mt. Graham, Arizona. Science done at the ARO includes the discovery of new molecular lines, the molecular properties of evolved stars and protoplanetary nebulae (SSE 3), characterization of ion chemistry, refractory chemistry, and organic chemistry in interstellar space, and the kinematics and chemistry of star-forming regions (PSF 1). As one of the few telescopes in the submillimeter VLBI network, the SMT was critical to the detection of Sgr A* at 1.3 mm, which constrained the orientations for an accretion disk (GCT 3; GAN 4). The ARO is currently not supported by the URO program. Observing time is available through collaborations with members of Steward Observatory.

Submillimeter Array (SMA)

The SMA consists of eight moveable 6-meter antennas on Mauna Kea, Hawaii. It is the first telescope capable of providing sub-arcsecond imaging at submillimeter wavelengths. The SMA studies the surfaces and atmospheres of solar system objects, magnetic-field structure in star-forming regions (PSF 1), properties of protoplanetary disks (PSF 2), the chemistry of evolved star envelopes, the supermassive black hole at the galactic center (including VLBI; GAN 4; GCT 3), the cool interstellar medium in nearby galaxies (GAN 2), and starbursts at cosmological distances (GCT 2). The SMA is a joint project of the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA). It has not been supported by NSF. Up to 30 percent of the Smithsonian share of observing time is open to the international community.

South Pole Telescope (SPT)

The 2001 decadal review committee (AANM) recommended construction of the South Pole Submillimeter-wave Telescope (SPST) for observations between 0.2 and 1 mm. The SPT is a project of the University of Chicago, the University of California at Berkeley, Case Western Reserve University, the University of Illinois, and the Smithsonian Astrophysical Observatory. A 10-m telescope has been constructed and is currently observing. The first instrument, a multifrequency bolometric camera, is aimed at detecting thousands of clusters of galaxies through the SZE and measuring the small-scale anisotropy in the CMB. Results of initial surveys are very encouraging. The Office of Polar Programs at NSF funds the SPT as an experiment, not as a facility that will be open to guest investigators.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×
RMS Facilities Currently Under Construction with U.S. Participation
Enhanced Very Large Array (EVLA)

A long overdue upgrade of the NRAO VLA, with help from Canada and Mexico, will be completed in 2012, and will result in a factor-of-10 improvement in continuum sensitivity and in broadband spectral-line access. The centimeter-wave sources studied with the EVLA will include jet emission associated with AGN and galactic micro-quasars (GCT 3), masers, and extragalactic H I emission, radio supernovae (GAN Discovery) and supernova remnants, free-free emission and radio recombination lines from star-forming regions in the galaxy (PSF 1) and beyond, and CO emission from high-z galaxies (GCT 2). The improvement in continuum sensitivity will make the EVLA sensitive to thermal sources of emission at the higher frequencies, allowing observations of free-free emission from compact objects and stellar photospheres. Upgrades to improve wavelength coverage and imaging would improve the capability for efficient high-resolution centimeter-wavelength imaging.

Atacama Large Millimeter Array (ALMA)

ALMA will be the largest ground-based astronomical facility ever built (Figure 9.7). Under construction in the Atacama Desert in northern Chile at an altitude of 5,000 meters, ALMA consists of a main array of 50 12-meter antennas, which are reconfigurable to allow a wide range of angular resolutions down to 4 milliarcseconds at submillimeter wavelengths. ALMA is supplemented by the Atacama Compact Array (ACA), which can image large-scale structures. ALMA is a partnership of Europe, North America, and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by NSF in cooperation with the National Research Council of Canada and the National Science Council of Taiwan (NSC), and in East Asia by the

FIGURE 9.7 Five antennas at ALMA’s high-elevation Array Operations Site (December 2009). SOURCE: Nick Whyborn, ALMA (ESO/NAOJ/NRAO).

FIGURE 9.7 Five antennas at ALMA’s high-elevation Array Operations Site (December 2009). SOURCE: Nick Whyborn, ALMA (ESO/NAOJ/NRAO).

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by NRAO, which is managed by Associated Universities, Inc. (AUI), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The North American partners are investing $500 million for construction and $30 million per year for operations and are entitled to ~35 percent of the observing time. The North American ALMA Science Center (NAASC) will provide full-service user support for the North American community. Three key science goals drive the ALMA specifications: (1) detect spectral line emission from CO or CII in normal galaxies at a redshift of z = 3, in 24 hours (GCT 2); (2) image the gas kinematics in protoplanetary disks around young Sun-like stars at the distance of the nearest star-forming clouds (PSF 1); and (3) provide high-fidelity images at an angular resolution of 0.1″ to match current OIR capabilities. With ALMA, one can use diagnostics such as thermal dust continuum emission, molecular rotational lines, and atomic fine-structure lines to study sources as diverse as planetary atmospheres, cometary nuclei, molecular cloud cores, protostellar jets, circumstellar and protoplanetary disks, the immediate environment of the galactic center supermassive black hole, and star-forming galaxies from the present day to z > 10 (PSF 1, 2; SSE 1, 3; GAN 1, 2; GCT 2, 4). Early science is expected to start in 2011, transitioning to full operations in 2013. Upgrades to achieve full wavelength coverage, when combined with EVLA coverage would, enhance this capability.

Large Millimeter Telescope (LMT)

The LMT is a 50-m telescope under construction at 4,600-m altitude on Sierra Negra in Puebla, Mexico. It is a collaboration of the Instituto Nacional de Astrofísica Óptica y Electrónica (INAOE) and the University of Massachusetts at Amherst. The LMT will observe dust and molecular gas from the solar neighborhood to high-redshift galaxies, providing key information on how stars form (PSF 1), the stellar initial mass function (PSF 1), how giant molecular clouds form and evolve in galaxies (GAN 2), how matter cycles into and out of galaxies (GAN 2), and how cosmic structures form and evolve via observations of the SZE (GCT 1). Large surveys and fast mapping speeds are essential to these science goals. Firstlight instruments have been completed and used as guest instrumentation on existing telescopes. The antenna structure and 32 m of the planned 50-m-diameter primary mirror surface have been completed, and integrated testing has begun. Commissioning was anticipated to begin in 2010. The LMT has a small amount of funding through the URO program.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×
Long Wavelength Array (LWA)

The long-wavelength portion of the electromagnetic spectrum is not well explored, particularly the transient sky. The Long Wavelength Array (LWA) is a unique U.S. facility aimed at this science. Situated in New Mexico, the LWA has a relatively quiet radio-frequency-interference environment, with partial access to the southern sky, and thus complements the European LOFAR effort. The primary goals of LWA are to survey the long-wavelength sky, to search for decametric emission from exoplanets, and to map the circumgalactic medium. The LWA is a joint effort of the University of New Mexico, the Naval Research Laboratory, Virginia Tech, the Jet Propulsion Laboratory, LANL, and the University of Iowa. The initial station, out of a planned 52, is under construction near the VLA site with funding from NRL; Phase 1 operations are expected in 2011. The proposed 52-station LWA would require additional funding; the 16-station core could be operating as early as 2017, and the full array by 2019.

The International Context

In the previous section and in Table 9.2, only facilities with U.S. funding are described. In this section the panel describes the international context in terms of providing the U.S. community with the capabilities it needs to meet the decadal science goals.

ALMA will be a powerful new facility, giving unparalleled sensitivity and resolution to the submillimeter and millimeter sky. But it has a restricted instantaneous field of view, several arcseconds across at the shortest wavelengths. The ACA provides some wide-field mapping capability for extended fields on arcminute scales at the longer wavelengths. However, taking full advantage of ALMA requires a finder scope, a very-wide-field submillimeter telescope for wide-area surveys, playing the role of the LSST for the GSMT in the millimeter/submillimeter region. During the past two decades the Europeans and the Japanese have moved actively into millimeter and submillimeter research, and recently into southern ALMA pathfinder telescopes. The French-German-Spanish IRAM operates two Northern Hemisphere facilities, a 30-m single-dish telescope located on Pico Veleta, Spain, and the Plateau de Bure Interferometer (PdBI), with six 15-m telescopes in the French Alps, for observing in the millimeter atmospheric windows. PdBI has 40 percent more collecting area than CARMA but fewer baselines for imaging, with restricted access to southern sources such as the galactic center. IRAM is seeking funding to expand the PdBI by doubling the number of antennas and the longest baselines, which would bring its sensitivity to within a factor of 3 of ALMA at 3 mm. The APEX (Atacama Pathfinder EXperiment) Telescope is a 12-m ALMA prototype antenna operating at Chajnantor near the ALMA site, equipped with

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

heterodyne receivers operating from 1.3 mm to ~210 μm, and bolometer arrays at 870 and 400 μm. APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, Onsala Space Observatory, and ESO. The ASTE (Atacama Submillimeter Telescope) is a 10-m telescope operated by Japan (NAOJ) at Chajnantor at 870 μm. The Chajnantor telescopes are important submillimeter pathfinders for the southern sky. Access by U.S. astronomers to these facilities is limited.

The 45-Meter Telescope of the Nobeyama Radio Observatory is a facility of the NAOJ in Japan that operates at 3 mm and can be used by U.S. astronomers with a Japanese collaborator (the Nobeyama Millimeter Array is no longer open for general observing). The James Clerk Maxwell Telescope, run by the Joint Astronomy Centre (United Kingdom, Canada, the Netherlands) is a 15-m telescope on Mauna Kea operating in the submillimeter. Its bolometer camera—the highly successful SCUBA, operating at 870 and 450 μm—was responsible for the discovery of submillimeter galaxies in the distant universe. Its successor, SCUBA-2, with a projected mapping speed a thousand times SCUBA’s, has recently received its science detectors. ESA’s Herschel Space Observatory is opening the part of the far-infrared-submillimeter spectrum blocked from the ground with deep surveys and spectroscopy; although this is a European-led mission, NASA has funded some instrumentation, and some key projects are led by U.S. principal investigators.

Pulsar observing is a key area for decadal research. For pulsar-timing experiments, sensitivity is important, requiring telescopes with large collecting areas, large bandwidths, and sites with low radio-frequency interference. Many centimeter-wave telescopes around the world can contribute to this effort, but Arecibo affords the highest precision time-of-arrival measurements. The GBT and the Parkes telescope (of the Australia National Telescope Facility) have the advantage of being at low-radio-frequency-interference sites. After 2014, the FAST Telescope (Five-hundred-meter Aperture Spherical Telescope), under construction in Guizhou Province, China, will allow very sensitive pulsar work, with a collecting area twice that of Arecibo, albeit initially with less bandwidth.

The ability to determine celestial positions and proper motions with a high degree of precision is a key decadal science goal. The VLBA is unique in providing a platform for precision astrometry at centimeter wavelengths. None of the worldwide VLBI arrays remotely approaches the capabilities of the VLBA—especially when it is augmented with the VLA, GBT, and Arecibo as station elements—in terms of sensitivity, high-frequency coverage, rapid switching for phase calibration, intrinsic resolution, and throughput of a dedicated and highly tuned instrument, as compared to a network such as the European VLBI Network, which is based on part-time use of inhomogeneous, general-purpose radio telescopes. Improvements to the VLBA as part of the NRAO development plan will put the VLBA even farther ahead of other arrays.

The future of centimeter-wave observing has been dominated by visions for

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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the Square Kilometer Array. As discussed below, the SKA has evolved into three instruments. Demonstration arrays for SKA-mid (3 to 100 cm) are under construction. The South African MeerKAT (Meer Karoo Array Telescope) is based on 12-m dishes with broadband, single-pixel feeds, with plans to have 80 dishes on 8-km baselines by mid-decade. The Allen Telescope Array (ATA) has taken a similar approach. The Australian SKA Pathfinder (ASKAP) uses 12-m antennas with a 30-beam array operating at L-band (λ ~ 16 to 40 cm) and plans for 36 antennas. The European project A3IV (Aperture Array Astronomical Imaging Verification) uses aperture arrays at L-band to synthesize very large fields of view. All three SKA-mid concepts (broadband single-pixel, L-band focal plane array, L-band aperture array) have great potential to inform the final design of SKA-mid (~3,000 15-m antennas).

The meter-wave portion of the spectrum is divided between epoch of reionization experiments and general-purpose facilities. There are currently four first-generation EoR observatories: LOFAR in the Netherlands, GMRT of the Tata Institute of Fundamental Research in India, and PAPER and the MWA by U.S. teams in western Australia (an initial deployment of PAPER will occur in South Africa). All four arrays are striving to detect, and provide rough characterization of, the power spectrum of EoR H I emission—qualitatively similar to COBE’s CMB power-spectrum constraints. The main concern for EoR power-spectrum instruments is achieving the extremely high spatial, polarimetric, and spectral purity needed to subtract foreground emission. Collectively PAPER and the MWA form the first-generation HERA-I experiment and are leading instruments in terms of both sensitivity and the development of the precision calibration needed for foreground subtraction. HERA-II is envisioned as a second-generation EoR experiment that will use lessons learned from the first-generation instruments of HERA-I to measure the EoR power spectrum in detail. There are no plans to expand either the GMRT in India or LOFAR in Europe into a HERA-II competitor.

The GMRT and LOFAR are also capable multipurpose low-frequency arrays, in which only the shortest baselines (<<1 km) and the 110- to 200-MHz band (z = 12 to 6) are used in EoR observing. The GMRT spans λ = 20 to 600 cm with 30 45-m dishes and baselines up to 25 km. LOFAR is under construction and features two aperture arrays covering λ = 4 to 30 m and λ = 1.2 to 2.7 m with baselines up to ~1,000 km. The lower-frequency capabilities of LOFAR are similar to those of the LWA project in New Mexico, although LOFAR is sited far north in a challenging radio-frequency-interference environment.

Current Capabilities Within the RMS Observatory Suite

The current suite of RMS facilities provides a broad set of functionalities that can address some of the science questions of the next decade. The panel briefly summarizes these capabilities below.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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  • Ultrahigh-resolution imaging and astrometry. Imaging at milli-arcsecond resolution is a requirement for many areas of astrophysics. The VLBA in concert with the EVLA provides such capability, but some science questions require higher frequencies (GCT 3, 4). The ability to measure astronomical coordinates with micro-arcsecond precision (GAN Discovery) allows the measurement of distances across the galaxy, including the galactic center, and the three-dimensional motions of nearby galaxies. This precision-astrometry capability is provided exclusively by the VLBA, and upgrades to receivers and bandwidth are needed.

  • Pulsar timing. Pulsar-timing experiments provide a promising way to measure gravitational waves (CFP Discovery). Centimeter-wave observatories with large collecting areas can do this: Arecibo, Green Bank Telescope, and the EVLA. However, the restrictions imposed by the observing cadences required for pulsar-timing experiments complicate observing on general-purpose telescopes, and while Arecibo is very sensitive, the declination limits are restrictive. Progress in pulsar-timing experiments would accelerate with a dedicated facility.

  • Efficient, high-resolution centimeter-wave imaging. Interstellar and circumgalactic gas structures require sensitive imaging in the centimeter continuum, for studies of synchrotron emission and magnetic fields (GAN 1, 2), and for the relatively weak 21-cm line of hydrogen (GAN 1, 2; GCT 2). Arecibo is the most sensitive H I mapper, but it has declination limits and more importantly, its 3′ beam at 21 cm is a good match only for galactic and local-universe H I studies. The EVLA would require two orders of magnitude more sensitivity to perform cosmological H I studies on arcsecond scales, and it has a relatively limited field of view. The ATA-42 has a wide field of view, suitable for large-scale mapping, but it also lacks sensitivity to detect H I on small scales and would require an increase of three orders of magnitude in collecting area to reach the level called for in Table 9.1.

  • Efficient, high-resolution millimeter/submillimeter-wave imaging. Studies of the emission from CO in galaxies at redshifts up to z ~ 3 and above comprise an essential element of studies of galaxy evolution (GCT 2). Redshifted CO lines can be observed with the EVLA and with ALMA, with sufficient spectral resolution to do galaxy kinematics. Many of the galaxies observable by ALMA will be nearly as bright at high redshifts as they are at lower redshifts, owing to the shift of the far-infrared spectral peak into the millimeter/submillimeter band, the “negative K correction” (GCT 2). Full wavelength coverage is needed to cover all redshifts.

  • Transient sources. The ATA-42 is currently the only RMS observatory with dedicated time for transient science, as opposed to transient follow-up. The time available for this purpose is limited by the minimal level of NSF support.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Potential to Lose Capabilities

In 2005, NSF initiated a senior review of its ground-based telescopes. Its recommendations with regard to RMS facilities, which are nearly all under the jurisdiction of NSF, are the following:2

Radio-Millimeter-Submillimeter Astronomy Transition Program. The National Astronomy and Ionosphere Center and the National Radio Astronomy Observatory, which are heavily subscribed by other communities, should seek partners who will contribute personnel or financial support to the operation of Arecibo and the Very Long Baseline Array respectively by 2011 or else these facilities should be closed.

In response to the senior review, NSF recommended a ramp-down in NSF funding of Arecibo from $10.5 million in 2007 to $4 million in 2011. The panel understands that the Arecibo Observatory leaders are actively pursuing other funding sources, but the prospects are very uncertain. The future funding of the VLBA is also uncertain, but efforts to find other funding are ongoing.

The panel has noted earlier that important capabilities identified by the SFPs are provided by these facilities. The pursuit of gravitational waves (CFP Discovery) is dramatically enhanced by Arecibo (Figure 9.8). The large sky visibility of the GBT is strongly complemented by the better sensitivity, though limited sky coverage, of Arecibo; both are needed to detect and study nanohertz gravitational waves. High-precision astrometry (GAN Discovery) is the exclusive province of the VLBA. If these two facilities do not obtain other sources of funds, capabilities that have been identified by two of the SFPs as key discovery areas will be lost. Since the time of the senior review, developments in the areas of transient astronomy and astrometry have dramatically changed the context in which these instruments are viewed. Because of the importance of Arecibo for pulsar timing and galaxy evolution, the panel recommends restoring $2 million per year to its baseline budget. The importance of astrometry likewise justifies continued support of the VLBA.

Capabilities Missing or Inadequate Within the Current Portfolio

Consideration of the science goals set forth by the SFPs reveals the following capability gaps in the current RMS portfolio (Table 9.3).

  • Sensitive meter-wave imager. Studies of the epoch of reionization require new capabilities at meter wavelengths.

  • A dedicated solar radio telescope. A radio complement to ATST would deliver full-disk images with rapid cadence over a wide range of wavelengths.

2

Information on the NSF 2005-2006 AST Senior Review is available online at http://www.nsf.gov/mps/ast/ast_senior_review.jsp. Accessed February 2011.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.8 The probability of detecting a stochastic background generated by an ensemble of supermassive black-hole binaries as a function of the energy density in gravitational waves (normalized by the closure density of the universe). The solid line assumes 20 pulsars, 12 observed with the Green Bank Telescope and 8 observed with Arecibo. The dashed line assumes 20 pulsars observed with the GBT alone. Both lines assume 5 years of observations, with two observations of each pulsar per month, for the same net telescope time. SOURCE: Fredrick Jenet, University of Texas, Brownsville.

FIGURE 9.8 The probability of detecting a stochastic background generated by an ensemble of supermassive black-hole binaries as a function of the energy density in gravitational waves (normalized by the closure density of the universe). The solid line assumes 20 pulsars, 12 observed with the Green Bank Telescope and 8 observed with Arecibo. The dashed line assumes 20 pulsars observed with the GBT alone. Both lines assume 5 years of observations, with two observations of each pulsar per month, for the same net telescope time. SOURCE: Fredrick Jenet, University of Texas, Brownsville.

TABLE 9.3 Capabilities Provided by Current Facilities

Capability

Current Facilities

Needed Development

Cosmic microwave background program

Existing program

Continue successful program

Sensitive meter-wave array

Demonstrators only

Factor-of-10 more area

Solar radio telescope

Demonstrators only

Full range, fast imager

Fast millimeter/submillimeter surveys

CSO until 2016

Bigger, faster, southern skies

Fast centimeter surveys

ATA-42, GBT, Arecibo

Expand ATA, multibeam GBT, Arecibo

Efficient high-resolution imaging centimeter/millimeter

VLA, soon EVLA, ALMA, CARMA

Enhance EVLA, ALMA, CARMA

Very sensitive centimeter imaging

None

About 1-square-kilometer area array

Dedicated pulsar timing, transients

Nothing dedicated, partial support from Arecibo, GBT

Expand ATA, enhance and dedicate time on Arecibo, GBT

Ultrahigh resolution

VLBA

Improve sensitivity, astrometric accuracy, develop millimeter/submillimeter VLBI

Complete wavelength coverage

EVLA, ALMA

Add missing bands

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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  • Fast millimeter and submillimeter survey instrument. ALMA will have a very limited instantaneous field of view, only arcseconds across at the highest frequencies. It can map larger fields at the longer wavelengths in combination with the ACA, but large-scale surveys—such as surveys of the galactic plane—would be extremely time-consuming and an unwise use of ALMA time. A large-field mapper operating at millimeter and submillimeter wavelengths is required to pave the way for higher-resolution follow-up observations with ALMA.

  • A very sensitive centimeter-wave imager. To image H I in galaxies beyond z of about 0.1 requires much greater sensitivity than even the EVLA achieves. Because receivers have reached their sensitivity limits, only collecting areas on the order of a square kilometer will provide this capability.

  • Dedicated transient instruments across the RMS spectrum. Transients by their nature require large amounts of dedicated survey time and flexibility in observing cadences. Predictable sources such as pulsars can be scheduled, albeit with some difficulty, along with traditional programs at existing telescopes. Serendipitous transients require a dedicated instrument.

  • Ultrahigh-resolution imaging in the millimeter and submillimeter. The ability to image Sgr A* in the radio regime free of scattering requires more sensitive submillimeter VLBI observations than are currently possible.

FUTURE PROGRAM

Introduction

The panel presents a future program that is balanced: across scientific fields; across wavelength regions; between capabilities for fast, wide-field surveys—enabled by large, single-dish telescopes equipped with new generations of large-format detector arrays—and for high-resolution, high-sensitivity studies of objects found in surveys. It is balanced among large national/international facilities, small university facilities, and PI-driven projects. The panel includes recommendations for technological developments and relevant laboratory and theoretical programs. The program includes innovative new facilities and cost-effective upgrades to existing facilities.

The RMS Panel was presented with a wide range of possible activities. In prioritizing the possible activities, the panel has been guided by the work of the SFPs. The panel used the reports of the SFPs to identify needed RMS capabilities (see Table 9.1). Then the panel summarized the capabilities that are supplied by existing facilities and identified the capabilities that are missing (see Table 9.3). In this section, the panel shows how the recommended program provides these capabilities, employing a combination of building new facilities and of sustaining

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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and developing current capabilities. The panel discusses some small and moderate programs that add needed capabilities and address some system issues. This panel’s final prioritization is done in the “Recommendations” section below.

New Facilities for Mid-Scale Funding
Hydrogen Epoch of Reionization Array (HERA)

The study of cosmic reionization is currently at the forefront of astrophysical research and is highlighted by the GCT Panel. In the epoch of reionization, fluctuations in neutral hydrogen trace directly the fluctuations in the matter density of the universe; observing these fluctuations provides new constraints on the physics of the early universe and the earliest luminous sources. These fluctuations can be observed only in the redshifted 21-cm emission from neutral hydrogen; hence, radio observations in the meter-wave range are a unique probe of this previously unexplored epoch of cosmic evolution.

To explore the EoR, a meter-wave array (1 to 3 m, or z = 5 to 15 for the H I hyperfine line) is needed (see Table 9.1). Such a capability would further enable studies of the solar corona and solar wind as well as searches for variable sources (another potential area of discovery). HERA provides a program to achieve such capabilities over the next decade and beyond in a staged approach.

The HERA program consists of three major steps (or stages). The goal of HERA-I is to detect the reionization signal and to measure a few of its most general properties, such as the power spectrum, over a limited range of spatial scales and cosmic redshifts. The HERA-I program is currently being actively pursued in the United States, spearheaded by the Murchison Widefield Array (MWA) and the Precision Array to Probe the Epoch of Reionization (PAPER), which are testing alternative approaches (Figure 9.9). The collecting area of each of these experiments is on the order of 0.01 square kilometers or less. Continued support of MWA and PAPER at about $5 million per year for about 5 years will be needed to complete the HERA-I stage.

The second stage of the program (HERA-II) aims at detailed characterization of the power spectrum of the fluctuations and other statistical measures of the signal. The HERA-II experiment will require approximately a factor-of-10 increase in the collecting area (to about 0.1 square kilometers).

The HERA-III stage aims at direct imaging of neutral hydrogen during the reionization epoch. Such an instrument would require on the order of 1 square kilometer of collecting area and is a natural candidate for the long-wavelength component of the Square Kilometer Array project. Even in the most optimistic scenario, construction of such a telescope cannot start earlier than 2020. HERA-II will set the stage for HERA-III.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.9 Left: Some elements of the Murchison Widefield Array. Right: Tilted data cube from a simulation of the reionization of the universe. The box is 1 Gpc h–1 on a side and is a periodic volume at redshift z ~ 9, when the universe was about half ionized in this model. Ionized regions are blue and translucent, ionization fronts are red and white, and neutral regions are dark and opaque. A random sampling of 5 percent (about 40,000) of all halos at z = 0 is shown as yellow points. Reionization is still quite inhomogeneous on these large scales, with large regions ionizing long before others. SOURCE: Left: MIT Haystack Observatory. Right: Marcelo Alvarez, Canadian Institute for Theoretical Astrophysics, University of Toronto.

FIGURE 9.9 Left: Some elements of the Murchison Widefield Array. Right: Tilted data cube from a simulation of the reionization of the universe. The box is 1 Gpc h–1 on a side and is a periodic volume at redshift z ~ 9, when the universe was about half ionized in this model. Ionized regions are blue and translucent, ionization fronts are red and white, and neutral regions are dark and opaque. A random sampling of 5 percent (about 40,000) of all halos at z = 0 is shown as yellow points. Reionization is still quite inhomogeneous on these large scales, with large regions ionizing long before others. SOURCE: Left: MIT Haystack Observatory. Right: Marcelo Alvarez, Canadian Institute for Theoretical Astrophysics, University of Toronto.

A crucial technological challenge for the HERA program is presented by the exquisite dynamic-range requirements. The expected cosmic signal is dominated by the system temperature and the foreground emission from the Milky Way and external galaxies. To remove these contaminants, the system calibration and the removal of the cosmic foregrounds must be achieved at about 1 part in a million precision. Such precision has so far only occasionally been obtained in radio observations; the success of both the HERA-I and HERA-II experiments will hinge on the ability of the project teams to achieve this precision routinely over extended periods of time.

The cost of HERA-II remains uncertain. The panel estimates a construction cost of $85 million, balanced between the cost in the plan presented by the HERA consortium and an independent cost analysis. The U.S. portion of the cost will depend on the in-kind and financial contributions from international partners, in particular Australia, where the HERA-II experiment may be located. The panel recommends an evaluation of HERA-I results in about 5 years. If specific milestones are met, there should be an open competition for HERA-II.

Frequency-Agile Solar Radiotelescope (FASR)

The study of stellar magnetism is the first question raised by the Panel on Stars and Stellar Evolution. In the words of that panel, the Sun “continues to be a work-

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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ing template for understanding magnetohydrodynamics and plasma physics ‘in practice’—physics that is crucial in many other arenas” (“Introduction” in Chapter 5, this volume). The panel identified a major contribution to this goal: a dedicated radio-survey instrument studying the Sun (see Table 9.1). Existing solar radio facilities such as NRAO’s Green Bank Solar Radio Burst Spectrometer (BSRBS) and NJIT’s Owens Valley Solar Array (OVSA) have demonstrated the potential of solar radio diagnostics for characterizing the strength and topology of magnetic fields in the Sun’s corona and for capturing the dynamics of solar eruptions and associated particle acceleration. However, to probe solar magnetism in detail with radio observations, the high-resolution imaging spectroscopy over three-and-a-half decades of wavelength (6 m to 1.5 cm) of the Frequency Agile Solar Radiotelescope is required (Figure 9.10).

FASR consists of three arrays: the A array covers 1.4 to 15 cm with an array of ~100 steerable 2-m antennas, spread over about 4 km; the B array covers 12 to

FIGURE 9.10 Artist’s conception of the FASR Array. SOURCE: Isaac A. Gary, New Jersey Institute of Technology.

FIGURE 9.10 Artist’s conception of the FASR Array. SOURCE: Isaac A. Gary, New Jersey Institute of Technology.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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100 cm with an array of ~70 steerable 6-m antennas, spread over about 4 km; the C array covers 1 to 6 m with 50 non-steerable antenna stations, each with a small array of electronically steered dipole antennas. All arrays are fixed in position. A prototype antenna for array A has been evaluated, and a costed design exists for the 6-m antenna. The correlator technology is not challenging.

FASR will produce a full Stokes spectrogram of the complete solar atmosphere with arcsecond resolution (λ/1.5-cm arcseconds), providing a CAT-scan-like probe of the temperature, density, and magnetic field, from the chromosphere through the corona, once every second. These observations will be unprecedented and will address the question of how magnetic fields power a star’s chromosphere and corona. Their full-Sun, continuous nature will enable FASR to act as a solar survey instrument. Its operational lifetime will span a 22-year solar magnetic-activity cycle, throughout which it will gather a rich database of solar eruptions. Thus FASR will be an essential complement to the Advanced Technology Solar Telescope, which provides high-spatial-resolution, but small field-of-view, coronal-magnetic-field observations. It will be unique in its ability to monitor magnetically driven transient activity across the solar disk and limb. Data-pipeline products, such as two-dimensional magnetograms of the coronal base to be produced each second, are planned to ensure broad access to the science observations. This will help to ensure synthesis with coronal observations at longer wavelengths and coordination with the modeling efforts needed for effective interpretation of the data.

FASR is a mature effort that has been recommended in two previous NRC decadal surveys. Extensive development and design reviews have been funded and achieved, including the testing of prototype instrumentation and the detailed planning of FASR operations, maintenance, and management. Independent analysis of FASR characterized it as “doable today.” It could be completed by 2015-2018. The ATST current schedule is for scientific operations to begin in 2017, and so the complementarity between ATST and FASR should be exploitable. The project cost was estimated at $68 million for construction; independent estimates put the cost at $109 million based primarily on higher estimates for project management, antennas, and reserves. The operations costs were estimated at $3 million per year (project) and $4 million per year (independent).

Because FASR science is intrinsically interdisciplinary—the fundamental astrophysical processes of magnetism and stellar dynamics that it probes have a direct impact on Earth’s space environment—it has excellent prospects for cross-directorate funding. Indeed, support to date has been split between two NSF directorates, Mathematical and Physical Sciences (which includes the AST division) and Geosciences (which includes the ATM—now AGS—division). FASR has a current “Pathfinder” proposal submitted to AGS with a budget of about $8 million that would demonstrate a limited subset of FASR’s science goals and could be upgraded

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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in stages to achieve the full FASR implementation. The evaluation of FASR has been based on its full implementation, which the panel judges to be ultimately necessary to achieve critical science goals. The panel adopted cost appraisals closer to those of the independent estimate, allowing for possible higher costs for antennas and a larger reserve than estimated by the project. The panel assumed a total cost of $100 million for construction and $4 million for operations, both split equally between NSF-AST and NSF-AGS. The panel recommends FASR with priority equal to that of CCAT.

CCAT

The GCT, GAN, and PSF reports identified a need for a fast millimeter/submillimeter survey instrument, which would provide essential input to ALMA observations (see Table 9.1). This need is met by a Southern Hemisphere, large-aperture submillimeter telescope equipped with large-format continuum detector arrays and spectroscopic instrumentation. The revolution in incoherent detector array technology will enable arrays with 105 to 106 detectors, each detector very sensitive because it is broadband. Such arrays cannot be used in interferometers, but on single-dish telescopes they can provide surveys of large areas, revealing rare objects—such as the recently discovered starburst QSO at z > 6—and large samples for statistical analysis. Such a survey telescope plays a role relative to ALMA analogous to that of the 48-inch Schmidt relative to the 200-inch Palomar telescope.

The proposed CCAT is a 25-m-diameter-aperture facility to be located near the ALMA site and designed to operate at submillimeter wavelengths (λ = 0.2 to 3 mm) (Figure 9.11). CCAT will be equipped with megapixel-scale detector arrays, enabling it to execute large-scale surveys and mapping with an exceptional continuum sensitivity of 2 mJy s0.5 per pixel at 1 mm. About half the observing time will be devoted to large surveys that will provide essential source catalogs for ALMA, with much less source confusion than smaller telescopes operating at longer wavelengths. Thus CCAT will complement surveys at millimeter wavelengths. NSF participation will ensure community access to the survey results.

In terms of SFP science drivers, CCAT will be able to (1) study structures of molecular regions; (2) identify young circumstellar disks via their submillimeter excesses; (3) survey young embedded submillimeter sources in dense molecular clouds and assess their relationship with the stellar initial mass function; (4) map thermal dust emission from nearby galaxies; (5) identify primeval submillimeter galaxies out to the epoch of stellar bulge and supermassive black hole buildup; and (6) detect large-scale structures in the early universe via the SZE. These CCAT wide-field surveys will drive much of the science to be done with ALMA. The eventual inclusion of multiobject spectrometers will enable early-universe galaxy-

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.11 Design of CCAT at its planned location 600 meters above the ALMA site. SOURCE: CCAT; see www.submm.org.

FIGURE 9.11 Design of CCAT at its planned location 600 meters above the ALMA site. SOURCE: CCAT; see www.submm.org.

redshift searches and detailed studies of star-forming regions and starburst galaxies. The potential technology risks are the maturity of focal-plane design and the pointing-control-system performance. These risks are correlated with image quality, which impacts sensitivity and the confusion limit of data. Detector development is progressing rapidly, however, as discussed below in the subsection “Technology Development.”

The project expects first-light in 2017, but an independent estimate suggested 2024. The panel believes that 2017 is more nearly correct if funding is available on the schedule requested. While ALMA will start operations before this time, it will operate for decades, and the panel expects ALMA to focus first on the brightest submillimeter galaxies, which will be found by other surveys. CCAT’s lower confusion limit will provide samples of galaxies to lower levels in the luminosity function that will be needed as ALMA matures.

The construction costs estimated by the project ($110 million) are similar to an independent estimate ($138 million with a 30 percent reserve). These estimates

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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include the costs of the telescope and optics, facility, software, initial instrumentation, and both project management and system engineering. Operations costs are estimated to be $10 million per year (project) to $11 million per year (independent). Note that only $33 million of the construction costs will be requested from NSF, with the rest coming from university and foreign partners. Based on independent estimates, the panel assumes an NSF share for operations and production of public databases at $7.5 million per year. Because the CSO, funded at $2.5 million per year, will close when CCAT opens, the cost increase will be $5 million per year.

The panel recommends participation at this level with priority equal to that of FASR.

Sustaining and Developing Current Activities

The new facilities recommended above leave some key requirements, as identified in Table 9.1, unmet. There is an excellent suite of existing telescopes, some new telescopes will be completed, and others will be upgraded in the coming decade. There are also ongoing programs that meet key science goals. What remaining needs could be satisfied by continuing successful programs or with upgrades and development on these telescopes?

The remaining capabilities that are needed to address the science questions are the following: a vigorous program of ground-based CMB studies; an instrument dedicated to transients and pulsar timing; fast-survey capability at centimeter wavelengths; improved sensitivity and wavelength coverage on high-resolution (0.1″ to 1″ resolution) imaging telescopes; and improved sensitivity at ultrahigh resolution (micro-arcseconds). In this section, the panel lays out a plan to achieve these capabilities by sustaining and developing current activities.

Studying the Cosmic Microwave Background

As a high priority, the RMS Panel recommends continuing a suite of measurements of the CMB temperature and polarization anisotropy. Although much has been learned from the study of the CMB, there is much more still to be learned. The CMB community is actively pursuing observations that will complement those from the Planck satellite and deliver exciting science throughout the decade (Figure 9.12).

A primary goal of large-angular-scale polarization measurements (θ > 1 deg, l < 200) is to measure the presence of primordial gravitational waves as revealed through the B-modes. The limit on B-modes may be improved by roughly a factor of five before multifrequency techniques are required to remove astrophysical foregrounds. Telescopes for the l < 200 measurements are ~1 to 2 m in size. The measurements are done from balloon (NASA) and ground (NASA/NSF/DOE)

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.12 The WMAP full-sky map of temperature fluctuations of the cosmic microwave background. The galactic signal has been subtracted. The lower-left inset shows the averaged temperature and polarization maps around temperature hot spots, and the lower-right inset shows those around cold spots. The characteristic polarization patterns—radial around hot spots and tangential around cold spots at about 1 degree from the temperature peaks—were predicted in 1994 and first observed in 2010. The patterns show the motion of baryonic gas into cold spots and out of hot spots in response to gravitational potential wells laid down at the birth of the universe. SOURCE: NASA/WMAP Science Team.

FIGURE 9.12 The WMAP full-sky map of temperature fluctuations of the cosmic microwave background. The galactic signal has been subtracted. The lower-left inset shows the averaged temperature and polarization maps around temperature hot spots, and the lower-right inset shows those around cold spots. The characteristic polarization patterns—radial around hot spots and tangential around cold spots at about 1 degree from the temperature peaks—were predicted in 1994 and first observed in 2010. The patterns show the motion of baryonic gas into cold spots and out of hot spots in response to gravitational potential wells laid down at the birth of the universe. SOURCE: NASA/WMAP Science Team.

platforms. The successful detection of the B-modes, which may occur within the decade, will require substantial confirmation. As the field matures, larger and more sophisticated detection techniques will have to be employed.

The primary goals of the small-angular-scale measurements of temperature and polarization (θ < 0.1 deg, l > 2,000) are to determine the parameters that characterize the primordial field (or fields), to quantify the cosmic neutrino content, and to measure the process of cosmic evolution with the SZE in thousands of clusters of galaxies. These angular scales are largely unexplored, but great strides can be made before the cosmology is limited by astrophysical foregrounds. The existing ACT (6 m) and SPT (10 m) efforts are part of this program and should continue to receive support.

The excitement of the science has driven the development of thousand-element cameras operating at 0.3 K, of superconducting electronics, and of compact coherent polarimeters. These developments will pave the way for a future satellite,

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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CMBPol, aimed at measuring the B-modes over the full sky with the accuracy attainable only with a dedicated satellite. The comparatively modest investment in the current ground-based and balloon program will significantly mitigate the risk for a future space program. The panel strongly endorses continuation of funding by NASA, DOE, NIST, and NSF’s Office of Polar Programs at least at current levels.

Allen Telescope Array Expansion (ATA-256)

The ATA plans to expand its current array from 42 elements to 256 elements (ATA-256) to provide roughly the collecting area of the GBT. Five key science surveys are planned to take advantage of the increase in sensitivity and resolution that the expansion will provide. In particular, the ATA-256 will be well equipped to time an array of pulsars in three to four different wave bands simultaneously, which is crucial for removing effects due to the interstellar medium, allowing the highest-precision measurements. This timing can also lead to valuable secondary science, such as measurements of neutron-star masses, tests of general relativity from relativistic binaries, and constraining the neutron star equation of state.

Currently, the ATA-42 is carrying out high-speed and wide-field-of-view surveys of the transient sky, but the ATA-256 will offer significantly improved sensitivity for transient science (Figure 9.13). The ATA-256 will be the only radio facility committed and dedicated to doing time-domain astronomy (GAN Discovery and SSE Discovery areas). In addition, transient searches will be able to be done commensally with pulsar timing, sensitive mapping of H I in the local universe, and SETI monitoring. Finally, the ATA-256 can play an important role as a precursor, large-N array for the SKA through lessons learned in operations, maintenance, signal processing, data management, and data archiving.

The ATA-256 consortium hopes to obtain funding for the expansion by early 2011, with full science operations to begin in late 2013. The ATA-256 consortium has estimated costs (based on the expenses incurred by building the ATA-42) to be $44 million over the decade for construction of the expanded array. After construction, it estimates $6 million per year for operations, maintenance, and survey science, of which up to 30 percent would come from private partner contributions. Independent cost appraisals were not available. The ATA-42 will carry out transition science during the construction and commissioning period as elements are added to the array at a lower operating cost of $3 million per year.

The ATA-256 has lower priority for mid-scale funding than HERA-II, CCAT, and FASR. If more money is available, or if HERA-I does not meet the milestones needed to proceed with HERA-II, ATA-256 would be the next priority after CCAT and FASR. Alternatively, expansion to 256 antennas could be treated as an upgrade, similar to those discussed below. The panel recommends that NSF explore partnerships with other agencies and private foundations to advance ATA-256.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.13 ATA-42 at the Hat Creek, California, site. SOURCE: Seth Shostak/SETI Institute.

FIGURE 9.13 ATA-42 at the Hat Creek, California, site. SOURCE: Seth Shostak/SETI Institute.

NRAO Development

An ongoing program of moderate, cost-effective, science-driven enhancements to NRAO telescopes can provide missing capabilities (see Table 9.1) that are essential to confront many of the key Science Frontiers Panel questions. The following non-prioritized developments will leverage the substantial capital invested in these telescopes and keep them on a path to new discoveries through the next decade and beyond.

EVLA

The panel supports a program of proposed enhancements to broaden greatly the EVLA capabilities: (1) E configuration, (2) Pie-Town link, (3) water vapor radiometers, and (4) long-wavelength-receiver system. The first three of these enhance the capability for efficient, high-fidelity imaging at centimeter wavelengths, while the fourth provides some meter-wave capability. The total cost is less than

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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$15 million plus $360,000 per year for operations. The technologies are mature, the timelines are short, and they carry little risk.

The E configuration ($8 million construction, $60,000 per year operations) will add 20 new antenna stations for higher surface-brightness sensitivity and better image fidelity at large angular scales, allowing new studies of H I in the galaxy and nearby galaxies (PSF 1; GAN 1, 2, 4), dense molecular cores and H II regions (PSF 1), and the SZE (GCT 1).

The Pie-Town link ($3 million construction, $80,000 per year operations) will improve the angular resolution by a factor of two, allowing studies of obscured and dense H II regions (GAN 2), protoplanetary disks (PSF 2), the mass-loss environment of massive stars, supernovae, and supernova remnants (SSE 2, 3), the AGN-starburst connection (GCT 3), and the structures, cores, and cusps of gravitational lenses (GCT 1; GAN 4).

The water-vapor radiometers ($1.2 million construction, $90,000 per year operations) will greatly enhance the phase stability at short wavelengths and long baselines, including the Pie-Town link, allowing studies of thermal emission from disks (PSF-2) and jets (GAN 1), the photospheres of supergiant stars (SSE 1), obscured H II regions and supernovae (GAN 2), and molecular lines at high redshift (GCT 3).

The long-wavelength receiver system ($1.8 million construction, $130,000 per year operations) will open up the observing window from 6- to 0.3-m wavelengths to allow studies of radio transients (GAN 5), magnetospheres of extrasolar planets (PSF 3), supernova-cloud interactions, (GAN 1, 2; SSE 2), steep-spectrum sources (GCT 3), radio relics and radio lobes (GCT 3), and atomic hydrogen and magnetic fields across cosmic time (GCT 1, 2). It is, however, not well suited to EoR observations.

GBT

The GBT combines large collecting area and good surface quality for sensitive, filled-aperture centimeter-wave observations (Figure 9.14). The panel supports the proposed, staged, array receiver and camera-development program. These upgrades will provide some of the needed capability for fast centimeter-wave surveys. The research and development costs are $31 million, and the production budget is $28 million, with $600,000 per year for operations. Much of the research, development, and production will be done at universities, supported by NSF grants. With sufficient funds for fundamental technologies, these new instruments can be realized in the next decade without high risk.

Three types of cameras are envisioned, including (1) a 100-pixel heterodyne camera for wavelengths of 2.6 to 4.3 mm and a 64-pixel heterodyne array for 10 to 17 cm, (2) a phased-antenna array for 20 cm, and (3) a 1,000-pixel bolometer

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.14 The Green Bank Telescope in West Virginia. SOURCE: NRAO/AUI.

FIGURE 9.14 The Green Bank Telescope in West Virginia. SOURCE: NRAO/AUI.

array for 3 mm, as well as associated efforts in integration and packaging of receiver elements, high-speed analog-to-digital conversion, and data transmission. These new instruments will enhance searches for gravitational waves using millisecond pulsars (CFP Discovery), studies of atomic and molecular gas content and evolution and astrochemistry throughout the Milky Way (PSF 1) as well as in galaxies nearby (GAN 1, 2) and at cosmological distances (GCT 2, 3), the characterization of galaxy clusters through the SZE (GCT 1), and the statistics of stellar remnant spins from pulsar timing (SSE 4, 5).

VLBA

The VLBA is a unique facility that provides ultrahigh angular resolution at radio wavelengths and has proved powerful for micro-arcsecond astrometry. Modest

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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upgrades will significantly expand this capability. The panel supports the proposed development package that includes (1) EVLA-style 4- to 8-GHz receivers, (2) wider data-acquisition bandwidths—to 4 GHz per polarization, and (3) water-vapor radiometers. The cost is about $16 million and carries little risk. These upgrades will significantly improve VLBA capabilities for astrometry (GAN Discovery) and will obtain accurate distances to large samples of star-forming regions throughout the galaxy, using 6.7-GHz methanol masers (PSF 1); measurements of Local Group motions to probe dark-matter content (GAN 4); and precision cosmology through a 1 percent determination of H0 using megamasers (CFP 2).

NAA

Looking to the future, the North American Array (NAA) initiative will pave the way for the U.S. community to lead the development and prototyping of the SKA-high. This $40 million investment is divided roughly equally between (1) developing enabling technologies, such as low-cost antenna concepts, wideband receivers, and data-processing capabilities, and (2) the implementation of a prototype NAA antenna station, perhaps at a location in New Mexico, that leverages the existing EVLA/VLBA infrastructure. This development package, in concert with international and national efforts aimed at longer wavelengths, will lay the groundwork for the United States to propose to grow SKA-high from the NAA in the 2020 decade.

ALMA Development

ALMA will be the world’s premiere facility for high-resolution imaging at millimeter/submillimeter wavelengths. It is essential that a program of upgrades be supported to maintain its vitality. While the upgrades will be determined by agreement of the international consortium, there are some obvious examples. Some receiver bands are not included in the first-light complement; adding these is important for obtaining complete wavelength coverage within atmospheric windows, which is especially needed for line studies of galaxies over the full range of redshifts. Adding capability to join the millimeter-wave VLBI network would greatly enhance the sensitivity for ultrahigh-resolution millimeter/submillimeter studies (see Table 9.1).

The consortium plans a program costing $90 million over a decade, of which $30 million would come from the North American partners. The panel fully supports this plan.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Small or Moderate Missions and Other Activities
Overview

A healthy RMS landscape will include small- and moderate-cost activities in addition to the major new initiatives and development of existing facilities. The panel supports in general a balanced program; a few particular activities that submitted responses to the survey’s request for information are discussed here. The panel looked among these for those that satisfied needs that were unmet by the larger projects.

The remaining capabilities that are needed to address the SFP science questions are the following: improved sensitivity at millimeter wavelengths for ultrahigh resolution (micro-arcsecond); and still better resolution at centimeter wavelengths. In this section, the panel lays out a plan to sustain and develop current activities.

Event Horizon Telescope

The Event Horizon Telescope will outfit and combine millimeter/submillimeter telescopes worldwide to directly image the black hole event horizon of SgrA* and the nearest active galactic nucleus in M87. It will also measure the black hole spin and constrain accretion and jet-launching models. The project is separated into three phases of development. The primary construction components include outfitting a number of existing telescope facilities with the requisite 0.85- and 1.3-mm receivers and VLBI capability, along with higher-bandwidth backends and data recorders. Observations would happen through few-week coordinated campaigns several times a year. Many of the required EHT upgrades will augment the science capabilities of the host facilities beyond the EHT program.

The current model-dependent measurements give the size of SgrA* at 1.3 mm as 3.7 (+1.6/−1.0) Rsch, where Rsch = 10 micro-arcseconds. The EHT aims for a resolution approaching 10 micro-arcseconds with sufficient sensitivity to make detailed images of the event-horizon environment. This has unique capability to image the region around an event horizon and explore fundamental black hole properties and physics. These goals are crucial for science questions GAN 4, What are the connections between dark and luminous matter?, and GCT 3, How do black holes grow, radiate, and influence their surroundings? The costs come in three phases (Phase I: $15.5 million; Phase II: $20.1 million; and Phase III: $11.5 million, anticipated to begin in 2019). The panel supports Phase I, with a reassessment at mid-decade. Phase I, with seven antennas operating at 1.3 mm, is expected to allow imaging and characterization of the central shadow predicted by general relativity, caused by the orbiting optically thin plasma, and to measure the orbital periods of material orbiting the central black hole to constrain the spin.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.15 CARMA with all three telescope sizes shown. SOURCE: John Carlstrom.

FIGURE 9.15 CARMA with all three telescope sizes shown. SOURCE: John Carlstrom.

CARMA Development

Hoped-for expansion of CARMA’s capabilities in the next decade includes a new, broadband, flexible, digital-correlator system, array receivers at 1 and 3 mm, and ultrawide-bandwidth receivers at 3 mm (Figure 9.15). The total cost of these development projects is $16 million. These upgrades will yield fast mosaicing speeds with a unique combination of high angular resolution and good surface-brightness sensitivity. The fast speeds will enable surveys of statistically large samples of molecular clouds for studies of star formation from the solar neighborhood (PSF 1) to nearby galaxies (GAN 2). The ultrawide-bandwidth 3-mm receivers will probe a broad range of redshifts in the early universe; for example, for z > 3, at least one CO line is always present in the proposed ultrawide 3-mm band. The flexible correlator would also allow sensitive, high-angular-resolution observations of the SZE (GCT 1) at 1 cm with unprecedented angular dynamic range (from 0.05 to 5 arcminutes using the OVRO, BIMA, and SZA antennas together). Large surveys are essential to achieve all of these science goals.

By enabling large surveys, by providing essential access for the U.S. community to interferometric observations to bolster ALMA observing-time proposals in a highly competitive environment, and by providing a crucial hands-on training ground for U.S. astronomers and students, CARMA will remain complementary to ALMA in the next decade. With its smaller size, CARMA has the ability to prototype and test future technology upgrades efficiently.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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SAMURAI

The SAMURAI (Science of AGNs and Masers with Unprecedented Resolution in Astronomical Imaging) project will substantially augment the scientific capabilities of the second-generation space VLBI station, VSOP-2, which is expected to be launched by the Japanese perhaps as early as 2013. VSOP-2 will observe at λ= 7 mm to 4 cm and achieve resolutions a factor of ~3 higher than ground-based VLBI. The U.S. project would focus on two science goals. The first is to determine the structure of radio emission from the accretion envelopes of black holes; at λ = 7 mm, SAMURAI will have a resolution of 40 mas, corresponding to 2 Schwarzschild diameters for Sgr A* and 7 for M87. The second goal is to provide precision astrometry of H2O masers in AGN that can be used to estimate distances precisely enough to improve the accuracy of H0 to 1 to 2 percent (CFP 3). SAMURAI and the VLBA provide complementary approaches to this critical measurement. The project requires construction of two ground-based tracking stations, use of existing U.S. stations, and other mission support. It also represents a contribution that will allow U.S. scientists access to the VSOP-2 program. In this sense the U.S. contribution is highly leveraged by Japan and the international community. The cost, $44 million, would be funded by NASA; thus the project falls outside this panel’s purview. The panel can only comment that this would help to provide the ultrahigh-resolution capability listed in Table 9.1 as necessary to addressing RMS-related science questions identified by the SFPs.

The RMS System and Community
The RMS System

The RMS “system” is quite different from the OIR “system.” NRAO operates national and international facilities that include only unique telescopes; older, smaller telescopes have been ruthlessly retired. A small number of University Radio Observatories provide complementary capabilities and hands-on training for students and postdoctoral scholars in both observing and instrumentation. Aside from the needed new capabilities discussed above, the major gaps in the RMS system are adequate funding for individual investigators and adequate support for the UROs.

Archives and User Support for RMS Facilities

With the data flow from ALMA, RMS science will enter a new era. The ALMA Science Archive will be the first full-service archive for RMS astronomy, and it will set the standard for such archives. Archival research, combining RMS data with data from other wavelength regions, will grow as the decade progresses. Full participation in Virtual Observatory protocols will be vital. NRAO has made some recent

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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efforts to help its users in this area. Computing was chronically underfunded in the early years of the VLA, and the VLA/VLBA has yet to achieve a user-friendly archive. There are efforts underway to provide an improved aperture-synthesis reduction-and-mapping package, CASA, for both the EVLA and ALMA, as well as for URO synthesis telescopes, and to provide a more user-friendly image archive.

Unlike the situation at the NASA great observatories, observing time on RMS facilities is not generally accompanied by funding for analysis and publication. NRAO supports page charges and has instituted a program to provide stipend and travel support for students using NRAO telescopes. While these efforts help, they do not provide the same level of support as the NASA facilities do for their users. The NASA support of guest investigators on HST alone dwarfs all user support for RMS facilities. This situation diminishes exploitation of expensive resources and makes it difficult for the United States to compete on the international stage. The panel reiterates the recommendation by the 2001 decadal survey AANM that NSF provide funding support for U.S. observers on its telescopes, whether international (e.g., ALMA), national, or a URO.

Training of Students and Postdoctoral Scholars

The training of the next generation of RMS scientists and instrumentalists takes place both at national facilities, such as the NRAO and NAIC telescopes, and at university radio facilities. National facilities mostly provide data, but there are some opportunities for hands-on operations by students, particularly at Arecibo and the GBT. The Jansky Postdoctoral Fellowships are the only prize fellowships directed toward RMS research. ALMA funds postdoctoral fellowships worldwide (mainly at ESO, NRAO, and NAOJ). The VLA and the GBT have modest programs that can support thesis research by graduate students. The GBT supports some visitor instruments and the concomitant instrumental experience back at their home universities. Research experience for undergraduates programs exist at a number of RMS sites. In the past decade, about 160 graduate students and 100 postdoctoral fellows have learned their craft while observing at the UROs.

Support for the UROs

The UROs are chronically underfunded. The RMS Panel met with a group representing currently funded UROs, along with groups that would like to be funded now or in the future. It was clear from the discussion and from later information gathered that the UROs provide not only vital capabilities but also the fundamental training grounds for future RMS scientists. Some scientists trained at UROs have been instrumental in transferring technology and techniques to other wavelengths. The panel strongly supports enhancements to the URO budget of $2 million per year for existing facilities and suggests that the URO system provide a mechanism

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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for operating new mid-scale facilities for which the panel recommended construction in this decade.

Technology Development

A strong and secure technology-development program is an essential component of a balanced RMS program. The panel recommends that the Advanced Technology and Instrumentation (ATI) program be enhanced by at least $1 million per year.

There are four major technology developments that can increase the speed of radio measurements by increasing the fields of view and the available bandwidths of both existing and future instruments.

  • Detector arrays. Millimeter and submillimeter bolometric arrays are opening several new scientific frontiers. Larger and more sensitive cameras promise to continue this revolution. A diversity of approaches in the power-detection, RF-coupling, and readout technologies has been a strength and should be supported, along with the continued development of total-power coherent detector arrays. Ongoing support is needed to continue the growth in detector elements shown in Figure 9.16.

  • Wideband digital systems. In the gigahertz range, advances in digital processing enable replacing analog RF mixers and filters with higher-performance digital complements, potentially decreasing costs and improving stability. At higher frequencies, the advent of 80-GHz samplers will lead to an increase in the available continuum and spectral bandwidth.

  • Large-N correlators. Several science goals require correlating thousands of inputs. This is especially important for observations of H I in high-redshift galaxies and epoch of reionization measurements, where the development of very-large-N correlators is the primary technical hurdle.

  • Phased-array feeds. Fully sampling the electric field across focal planes could significantly enhance the survey speed of both single-dish and interferometric instruments.

The panel encourages, whenever possible, including astronomical observations as part of technology assessment. Scientific observations with new instruments can significantly enhance the careers of students and postdoctoral associates, helping to replenish the pool of those with knowledge of state-of-the-art instrumentation.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.16 “Moore’s law” for submillimeter detectors showing a doubling time for a number of elements of about 20 months (dashed line). SOURCE: Jonas Zmuidzinas, California Institute of Technology.

FIGURE 9.16 “Moore’s law” for submillimeter detectors showing a doubling time for a number of elements of about 20 months (dashed line). SOURCE: Jonas Zmuidzinas, California Institute of Technology.

Laboratory Astrophysics

A wide range of new RMS facilities that are currently operating (e.g., spectrometers on the Herschel Space Observatory) or coming on line in the next decade will provide unprecedented access to diagnostic astrophysical spectral lines at sensitivities that may be 10 to 100 times better than those of current instruments (Figure 9.17). Even with current sensitivities, 30 to 50 percent of lines remain unidentified. To interpret anticipated data, improved information on frequencies, collision rates, and chemical reaction rates is needed. Key measurements include rest-frequency assignments for all known molecules (including vibrationally excited states and isotopologues); predicted spectral-line intensities and their temperature dependence; collisional excitation rates; isotopic-fractionation, photolysis, and dissociative-recombination branching ratios; binding and diffusion energies for molecules on ice surfaces; and activation energies for reactions. Some of these parameters (notably collisional excitation rates and potential surfaces for molecules) rely primarily on theoretical calculations.

Historically, many of the advances in laboratory astrophysics have been funded outside typical astronomy funding lines, for example in NSF’s physics and chemistry divisions. Unfortunately, these divisions are understandably reluctant to divert significant funds for activities that are directed primarily at astronomy. NASA has

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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FIGURE 9.17 Submillimeter Array 1.3-mm spectra from three dust cores (each plotted in a different color offset in the y-axis for clarity) in the massive star-forming region NGC6334I (sources are separated by only 2 arcseconds or about 4,000 AU) show tremendous chemical complexity over small size scales as well as a large fraction of unidentified lines. SOURCE: Todd R. Hunter, National Radio Astronomy Observatory.

FIGURE 9.17 Submillimeter Array 1.3-mm spectra from three dust cores (each plotted in a different color offset in the y-axis for clarity) in the massive star-forming region NGC6334I (sources are separated by only 2 arcseconds or about 4,000 AU) show tremendous chemical complexity over small size scales as well as a large fraction of unidentified lines. SOURCE: Todd R. Hunter, National Radio Astronomy Observatory.

provided some directed funding for laboratory astrophysics in support of a few missions, for example the Herschel Space Observatory, but that funding has been limited and of relatively short duration. In the coming decade, it is critically important that the astronomical community find a way to provide sustained support for laboratory astrophysics, potentially through cross-divisional NSF funding initiatives or directed funding lines within the astronomy division. The full scientific potential of the next generation of RMS facilities will be severely compromised without a commensurate dedication of resources to laboratory astrophysics. The panel recommends a program funded at $2 million per year.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Theory for RMS-Related Science

The panel lists below in two categories some theoretical needs that are especially important for RMS science.

The theoretical developments required for extracting science from RMS observations are the following:

  • Theoretical calculations of fluctuations in the intensity and polarization of the cosmic microwave background are an inherent part of deriving cosmological constraints from the CMB data.

  • Numerical simulations of cosmic reionization are needed to predict observables for redshifted 21-cm experiments (especially for the first stage, HERA-I). Given the potential complexity of foreground removal and accurate calibration, without such modeling the observational measurements of statistical properties of the cosmological signal (such as the power spectrum) will remain inconclusive until actual imaging capabilities are developed.

  • Full three-dimensional modeling of circumgalactic environments is crucial for the correct interpretation of the spectroscopic data. Without such modeling, differentiation between hot-gas accretion, outflows, virial shocks, and gas flows along filaments is extremely difficult or impossible.

  • Chemo-dynamical models of star-forming regions that trace the simultaneous evolution of density, gas and dust temperature, and molecular abundances through the evolution of a particular dynamical model are necessary for a correct interpretation of molecular-line observations.

  • Spectropolarimetric and magnetohydrodynamic forward modeling of the solar atmosphere in three dimensions will be essential to exploit the full potential of FASR data.

  • Interference mitigation will be critical, especially for low-frequency observations.

In several other areas, major theoretical development will be required to fully realize the investment in an RMS facility:

  • Modeling cosmological structure formation in representative cosmological volumes with resolution adequate to include the most of the important physical processes in the ISM.

  • Modeling black hole accretion on a wide range of scales, from the inner edges of accretion disks to global galactic environments.

  • Theoretical studies and numerical modeling of MHD processes on a wide range of scales, from the small-scale physics of reconnection and particle acceleration to the effects of magnetic fields on galactic and extragalactic scales.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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  • Numerical modeling of radiative transfer in galactic simulations, in simulations of star-forming regions, and in models of black-hole environments.

  • Precision modeling of stellar pulsations.

  • Theoretical studies and numerical modeling of planet formation, evolution, and dynamics in a range of environments.

  • Modeling of radiative and dynamical processes in planetary atmospheres.

  • Modeling of gravitational-wave signatures expected from stochastic backgrounds and from individual sources which could be detected by pulsar-timing arrays.

Algorithm Development

Many of the scientific goals for the next decade rely on the development of new algorithms that will facilitate the processing of large datasets, allow the discovery of weak signals, and foster cross-disciplinary data sharing. The most critical needs are as follows:

  • Foreground removal for epoch of reionization studies.

  • Optimal detection and characterization of gravitational-wave signals in pulsar data.

  • Computationally efficient pulsar-search algorithms to handle large amounts of data with sensitivity to the most relativistic binary systems and weak transients. Real-time search algorithms are imperative given the expected data rates of new correlators and multi-pixel receivers.

  • Spectral-line-analysis tools that aid in the identification of lines, extraction of line parameters, and analyses of physical conditions using laboratory astrophysics results and radiative-transfer algorithms.

  • Automated source-detection algorithms in the spectral domain to aid in the creation of source catalogs in formats compatible with Virtual Observatory standards.

  • Imaging algorithms that keep pace with the cutting edge of possible data rates through parallelization and high-performance computing possibilities.

A crucial need for RMS is greater access to high-speed data transmission for data acquisition and retrieval as well as access to long-term storage. Many of the proposed facilities can produce data at rates approaching a petabyte an hour. Innovative solutions for storage and public access, in keeping with observatory policies, are necessary. Strong partnerships between the NSF-AST division and the NSF Office of Cyberinfrastructure, as well as international agreements, will facilitate these goals.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Spectrum Management

The radio spectrum is a precious resource for radio astronomy and for communication in the modern world. Without continued vigilance to protect some of this resource for passive scientific use, radio astronomy from Earth’s surface will become increasingly difficult. The traditional approach of seeking protection for small, defined segments of the spectrum for radio astronomy is no longer adequate because of the wide bandwidths needed for sensitivity and the broad frequency coverage needed for spectral-line studies at high redshifts. Resources must be made available to develop modern technologies for radio-interference mitigation and for sharing the spectrum through time- and frequency-multiplexing methods.

Looking to the Future

The Square Kilometer Array is seen as the next-generation centimeter-wave and meter-wave telescope, which would address many fundamental science questions. This project has already garnered significant international support, with 55 institutions in 19 countries participating. The 2001 decadal survey recommended that the U.S. participate in a program of technology development funded at $22 million; $12 million has been funded, starting in 2007.

Over the past decade, the SKA has evolved into three instruments covering three wavelength regimes: SKA-low (1 to 3 m); SKA-mid (3 to 100 cm); and SKA-high (0.6 to 3.0 cm). The panel believes that it is very important for the United States to play a role in this international project. However, based on the information received from the projects and from independent analysis, none of the parts of this project have reached maturity sufficient to recommend construction at this time. Defining the way forward in this context requires a mix of technology development, demonstrator projects (e.g., LWA, MWA, PAPER, LOFAR, MeerKAT, ASKAP), and careful consideration of priorities. The results of the demonstrators will not be available for a number of years.

The long-wavelength (1.0 to 3 m) part of the spectrum covered by SKA-low provides the only way to study the process of reionization (H I at z = 5 to 14); through that, it is one of the most promising ways to study the first luminous objects (GCT 4). The HERA activity provides a step-by-step path for the U.S. community to lead in this exciting aspect of SKA science. It lays out a sequence of intermediate science and associated technology goals that address this key science area.

The mid-wavelength (3 to 100 cm) part of SKA provides the capability for very sensitive centimeter-wave imaging. SKA-mid is essential to study the role of atomic gas in galaxy evolution (GCT 2; GAN 1); it could provide spectroscopic imaging of the H I emission for a billion galaxies out to z ~ 1. This cannot be done with present facilities and is strong justification in itself for this ambitious instrument. SKA-mid

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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could address other key scientific questions as well: it would enable a powerful pulsar machine that would enable a census of the galactic pulsar population (SSE 4), test general relativity in the strong-field regime (CFP 2), and almost certainly detect low-frequency gravitational waves and constrain gravitational-wave sources (CFP 1, Discovery). It would provide excellent sensitivity to the transient radio sky (SSE Discovery).

In spite of the compelling science case for it, the panel finds that there are substantial issues of technical readiness and cost for SKA-mid. The total construction cost of the project, already $2.2 billion in the project’s estimate, was raised to $5.9 billion by independent analysis. SKA-mid was considered not technologically ready in the independent analysis, and the panel concurs. Further development and study of alternative options for this wavelength range are needed and could be funded in open competition within the ATI program, potentially in conjunction with other international efforts. Pathfinders, such as ATA-256, could help to test technical concepts that would lead to the final design of the SKA. Alternative approaches to constraining dark energy, such as 21-cm intensity mapping, could be explored to see if they can be useful on shorter timescales and at lower cost. The panel recommends revisiting the SKA design costs in 5 years to assess end-of-decade feasibility.

The short-wavelength (0.6 to 3.0 cm) part of SKA helps constrain dark energy (CFP 2), dark matter (CFP 3), galaxy evolution via CO and other molecules at z above 1.3 (GCT 2), planet formation (PSF 2), and the ends of massive stars (SSE 3). Because of the U.S. heritage with EVLA, GBT, VLBA, and ALMA, it is natural for the United States to build on these in developing this part of SKA. A modest program of technology development and prototyping should begin in this decade. The NAA activity discussed above provides an attractive way to proceed.

RECOMMENDATIONS

The panel recommends a program with three new major initiatives for mid-scale funding, upgrades to existing and imminent facilities, and increased funding for smaller facilities. The panel identifies a need for technology development in four main areas and an interdisciplinary laboratory astrophysics program, along with theory and algorithm development relevant to RMS science. The panel’s recommendations are made in the context of the following assumptions: a 7 percent per year increase in the NSF-AST budget and the augmentation of a funding line for mid-scale construction projects of at least $20 million per year. The panel recommends no projects for MREFC funding.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Major New Initiatives

The major new initiatives are HERA, CCAT, and FASR. In terms of scientific importance, the panel ranks HERA first, with CCAT and FASR tied and close behind. However, there are issues of readiness that require a distinction between ranking and phasing of project starts.

Of these, FASR is the most ready to proceed and, as the panel has noted, has excellent prospects for cross-directorate funding. The panel recommends that a funding strategy for FASR be developed with core contributions from both NSF-AST and NSF-AGS (the panel assumes here an even split). The FASR Pathfinder proposed by the project to AGS ($8 million) would be a good way to begin and resolve any remaining cost questions, but it should proceed in a manner that is ultimately compatible with the full implementation of FASR. The $50 million from AST would come from the mid-scale line starting in 2010 and ending in 2015. The 50 percent AST share of operations ($2 million per year) could come from an increase in the URO budget.

CCAT is also far along in design. The project, a consortium of U.S. and foreign institutions, estimated a total cost of $110 million, and the independent estimate was $138 million for construction. Of this, the consortium requested only $33 million from NSF. The panel recommends proceeding with this project as soon as the design is finalized and the consortium has the balance of the funding or suitable guarantees. There is substantial urgency in this project, because it will provide sources to optimize use of ALMA. CCAT would be an ideal candidate for funding by a mid-scale funding source when it becomes available, but it should start by 2012. It should phase in after FASR and complete funding by 2017. Operations costs from NSF will be $7.5 million per year, but shutting the CSO will save $2.5 million per year, and so $5 million per year extra will be needed in the URO budget by 2018 (see below).

HERA has the panel’s top science ranking, but it comes in three phases. The first phase, HERA-I, is underway with two parallel efforts engaged in testing techniques. The panel strongly recommends continued funding for both these efforts at a combined rate of approximately $5 million per year to about 2015, at which time a review would be needed. If the HERA-I projects achieve certain milestones, the panel would strongly favor funding of HERA-II, or a similar project selected in open competition, from the mid-scale funding line. The milestones are demonstration of successful techniques for calibration and foreground removal; detection of the power spectrum of H I in the epoch of reionization; a decision on the optimum design for HERA-II; and development of a full proposal for HERA-II with credible costs. The current estimates of cost for a mid-decade start for HERA-II range from $80 million to $115 million, but they depend strongly on future correlator developments. There should be further technology development toward HERA-III,

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
×

which would be a future-decade project. For HERA-I, the costs are a continuation of current funding, and so the panel counts only HERA-II as new funding and assumes a total cost of $85 million from the mid-scale line, starting in 2015 and ending in 2020. The panel assumes no operations funding this decade.

Sustaining and Upgrading Current and Imminent Facilities

The panel’s top priority in the facilities area is continued funding of a vigorous, diverse program of ground-based research on the cosmic microwave background. Detection of the so-called B-modes, which trace primordial gravitational waves, is a primary goal. The program should also constrain cosmological parameters, determine or limit the sum of neutrino masses, and measure large-scale structure. Since this is an ongoing program, it does not represent new costs, but the panel emphasizes its absolute importance.

The current ATA-42 is in serious need of funding. This project has pioneered the concept of large arrays of inexpensive antennas with broadband imaging response. Its current NSF support is inadequate to keep the current array running, much less to continue the technological evolution of the array to 256 antennas. The observing capabilities provided by the ATA-256 would provide major advances in the ability to find transients and detect gravitational waves. Moreover, this project can provide valuable technological developments for a mid-range SKA, in the area of wideband feeds, large-field imaging, and large-correlator development. The panel could not fit the funding for ATA-256 into a $20 million per year mid-scale line, but it would be the preferred back-up for such funding should HERA-I not meet its milestones. ATA-256 may be able to attract further funding by private foundations or other agencies. The panel recommends an effort to explore ways to move forward with a modest investment of NSF funds. This is the second priority in this category.

The panel recommends a regular program of upgrades for existing facilities, including ALMA, NRAO facilities, Arecibo, and elements of the UROs program. These upgrades will provide some of the capabilities identified as needed to answer the science questions. In particular, such upgrades are the most cost-effective way to obtain the capability for efficient high-resolution imaging at centimeter wavelengths and improved sensitivity with ultrahigh resolution (see Table 9.1). Multifeed arrays on the GBT and CARMA provide test beds for new techniques. Convincing cases were made for a total of $90 million over the decade for each of ALMA (the U.S. share is $30 million) and NRAO. The current UROs need more operating funds to improve their utility to the larger community (the panel recommends an extra $2 million per year) and further increases (ending the decade with an increment of $9 million per year) once FASR and CCAT become operational.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Because of the importance of Arecibo for pulsar timing, the panel recommends restoring $2 million per year in funding to its baseline budget.

Small Projects

Keeping a balance between large projects and national/international facilities and smaller projects is vitally important. Examples of excellent projects of this kind are the enhancement of millimeter-wave VLBI to create the Event Horizon Telescope, adding the huge collecting area of ALMA, and the addition of multifeed receivers to the CARMA telescopes. The panel recommends a total of $25 million for this effort over the decade, most likely funded by ATI or MRI.

The RMS System

Funding for user support and archive exploitation is important to the operation of the RMS system. The panel also recommends enhancements to the ATI program (by $1 million per year) that will allow more technology development for the future. The panel also recommends a program of laboratory astrophysics ($2 million per year) in which similar programs can be evaluated in context. RMS-related science depends heavily on laboratory and theoretical advances. Strategic theory and algorithm development should be supported to maximize the return on investments in facilities.

Summary

With a combination of new facilities and the sustenance and invigoration of existing programs and facilities, almost all the RMS capabilities needed to answer the science questions posed by the Astro2010 Science Frontiers Panels can be realized (Table 9.4, Figure 9.18). The most notable exception is the capability for very sensitive centimeter-wave imaging, needed for the study of H I at redshifts of 1 to 2. That requires something like SKA-mid, and the panel recommends some steps toward that goal. The panel summarizes in Table 9.5 the additional costs to NSF-AST for construction and operations. Table 9.5 indicates which items would be suitable for mid-scale funding and prioritizes projects costing at least $30 million.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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TABLE 9.4 Needed RMS Capabilities and the Panel’s Recommended Actions

Capability

Recommended Action

Cosmic microwave background program

Continue successful program

Sensitive meter-wave array

Continue HERA-I, fund HERA-II mid-decade

Solar radio telescope

Construct FASR

Fast millimeter/submillimeter surveys

Participate in construction, operations of CCAT

Fast centimeter surveys

Enhance ATA, GBT, Arecibo

Efficient high-resolution imaging at centimeter/millimeter

Enhance EVLA, ALMA, CARMA

Very sensitive centimeter imaging

Cannot meet this decade, technology development

Dedicated pulsar timing, transients

Enhance ATA, Arecibo, GBT

Ultrahigh resolution

Enhance VLBA, millimeter-wave VLBI

Complete wavelength coverage

Enhance ALMA

FIGURE 9.18 Mapping of required capabilities to new initiatives, upgrades of existing facilities, and continuation of successful programs. Dashed arrow indicates that need cannot be met this decade.

FIGURE 9.18 Mapping of required capabilities to new initiatives, upgrades of existing facilities, and continuation of successful programs. Dashed arrow indicates that need cannot be met this decade.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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TABLE 9.5 Added Costs to NSF-AST for Construction and Operations (FY2009 million dollars)

Action

Construction (total)

Priority

Operations (per year)

Continue HERA-I, construct HERA-II

85a

1

0

Construct FASR (50 percent AST)

50a

2, tie

2, starting 2015

Participate in construction, operations of CCAT

33a

2, tie

5, starting 2017

Enhance ATA if possible

44b

4

3, increasing to 6 in 2015

Enhance GBT, EVLA, VLBA

90c

5, tie

1

Enhance ALMA

30c

5, tie

 

Enhance CARMA, EHT

25c

 

 

Enhance UROs support

 

 

2

Enhance Arecibo support, if possible

 

 

2, starting in 2012

Enhance ATI

 

 

1

Laboratory astrophysics

 

 

2

Total over decade

357

 

131

aMid-scale funding.

bMid-scale or other funds for upgrades.

cSome elements could be mid-scale instruments; others could be MRI or ATI.

Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Page 495
Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Page 497
Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Suggested Citation:"9 Report of the Panel on Radio, Millimeter, and Submillimeter Astronomy from the Ground." National Research Council. 2011. Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics. Washington, DC: The National Academies Press. doi: 10.17226/12982.
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Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics Get This Book
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Every 10 years the National Research Council releases a survey of astronomy and astrophysics outlining priorities for the coming decade. The most recent survey, titled New Worlds, New Horizons in Astronomy and Astrophysics, provides overall priorities and recommendations for the field as a whole based on a broad and comprehensive examination of scientific opportunities, infrastructure, and organization in a national and international context.

Panel Reports--New Worlds, New Horizons in Astronomy and Astrophysics is a collection of reports, each of which addresses a key sub-area of the field, prepared by specialists in that subarea, and each of which played an important role in setting overall priorities for the field. The collection, published in a single volume, includes the reports of the following panels:

  • Cosmology and Fundamental Physics
  • Galaxies Across Cosmic Time
  • The Galactic Neighborhood
  • Stars and Stellar Evolution
  • Planetary Systems and Star Formation
  • Electromagnetic Observations from Space
  • Optical and Infrared Astronomy from the Ground
  • Particle Astrophysics and Gravitation
  • Radio, Millimeter, and Submillimeter Astronomy from the Ground

The Committee for a Decadal Survey of Astronomy and Astrophysics synthesized these reports in the preparation of its prioritized recommendations for the field as a whole. These reports provide additional depth and detail in each of their respective areas. Taken together, they form an essential companion volume to New Worlds, New Horizons: A Decadal Survey of Astronomy and Astrophysics. The book of panel reports will be useful to managers of programs of research in the field of astronomy and astrophysics, the Congressional committees with jurisdiction over the agencies supporting this research, the scientific community, and the public.

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