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Report of the Panel on Radio and Submillimeter-Wave Astronomy



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Astronomy and Astrophysics in the New Millennium: Panel Reports 4 Report of the Panel on Radio and Submillimeter-Wave Astronomy

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Astronomy and Astrophysics in the New Millennium: Panel Reports SUMMARY Radio astronomy covers five orders of magnitude in wavelength (300 mm to 30 m) and provides unique as well as complementary windows on the origins of the universe, galaxies, stars, and planets. Radio astronomers sample milliarcsecond scales and millisecond periods. Radio astronomers alone can view the early universe directly through the cosmic microwave background (CMB) and probe large-scale structure independent of redshift using the Sunyaev-Zel’dovich (SZ) effect. Radio waves offer the only clear view of the earliest stages of star and planet formation, both locally and in distant galaxies, by directly probing the dust, magnetic fields, gas dynamics, and rich molecular complexity in the highly obscured environments where galaxies, stars, and planets form. Not surprisingly, astronomy in the radio and submillimeter wavelength range is driven by technology advances. The last decade has seen the success of the Cosmic Background Explorer (CORE); the completion of the Very Long Baseline Array (VLBA); the launch of the Japanese Very Long Baseline Interferometry (VLBI) Space Observatory Program (VSOP) mission, which pioneered the technique of very-long-baseline interferometry from space; the upgrade of the Arecibo telescope; and the development of millimeter-wave interferometry and submillimeter capabilities. The Green Bank Telescope (GBT), a unique and powerfully flexible instrument exploiting new technology for radio-wave active optics, was dedicated in August 2000. The Atacama Large Millimeter Array (ALMA), the first-ranked major project of the Astronomy and Astrophysics Survey Committee’s Panel on Radio Astronomy a decade ago (it was known then as the Millimeter Array), is currently approaching its construction phase.1 The ALMA project is far more exciting and capable than originally envisaged and will provide the means to explore the dusty sites of planet and star formation and the hearts of the earliest galaxies. The Panel on Radio and Submillimeter-Wave Astronomy reaffirms the high priority given to ALMA by the 1991 Astronomy and Astrophysics Survey Committee and emphasizes that its construction schedule should be maintained. The panel recommends as its highest priority for major new funding 1   Astronomy and Astrophysics Survey Committee, National Research Council. 1991. The Decade of Discovery in Astronomy and Astrophysics (Washington, D.C.: National Academy Press).

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Astronomy and Astrophysics in the New Millennium: Panel Reports the Expanded Very Large Array (EVLA). While the Very Large Array (VLA) remains the most powerful and productive centimeter-wave telescope in the world, advances in technology make possible an order-of-magnitude improvement in both sensitivity and angular resolution, combined with a more than 1000-fold improvement in spectroscopic capability. The new EVLA will be an essential tool for astronomers investigating a wide range of scientific problems. For example, submillimeter studies have shown that a substantial part of the energy release at high redshifts occurs in regions obscured by dust, but the origin of the energy is in question. The EVLA will uniquely distinguish between massive star formation and accretion onto a supermassive black hole as the underlying energy source, allowing researchers to decode the history of star and galaxy formation as well as the role of supermassive black holes in galaxy evolution. The panel recommends the following moderate projects2 in order of priority: A well-orchestrated technology development program leading to the future construction of the Square Kilometer Array (SKA), an international next-generation radio telescope; Immediate construction of the Combined Array for Research in Millimeter-wave Astronomy (CARMA), to precede and ultimately to complement ALMA; Development of the Advanced Radio Interferometry between Space and Earth (ARISE) mission for space VLBI to achieve the highest spatial resolution at centimeter and millimeter wavelengths; and Construction of a large, single-aperture telescope at the South Pole equipped for wide-area surveying at submillimeter wavelengths, the 10-m South Pole Submillimeter Telescope (SPST). The panel emphasizes that continued investment in the pursuit of a complete understanding of the CMB, particularly its polarization properties, is critical. A host of experiments—on the ground, balloon-borne, and in space, including the Microwave Anisotropy Probe (MAP) and Planck missions—will characterize the CMB anisotropy within the next few years. Detection of the signature of gravitational waves on the CMB 2   Capital costs in the range $5 million to $50 million.

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Astronomy and Astrophysics in the New Millennium: Panel Reports polarization would provide a unique measurement of the energy scale of the inflationary potential, allowing the origin of the Big Bang to be explored. Radio astronomers will probe energy scales of 1016 GeV, well above the reach of particle accelerators, with a sensitivity to the gravity-wave background well beyond that possible with direct gravity-wave detectors. Discoveries by the MAP and Planck missions as well as ground-based investigations will suggest the direction for follow-on NASA missions. NASA should take the necessary steps to initiate those missions rapidly when the optimal strategy becomes clear. The panel endorses construction of the Low Frequency Array (LOFAR), an international and interagency project. This unique instrument will provide the first real capability to image the low-frequency (meter- and decameter-wave) sky and, along with the One Hectare Telescope (1HT), will constitute the first of the stepping-stones to the SKA. The panel further recommends an aggressive and vigorous program of technology development. SKA development activities should focus on low-cost, high-performance electronics and processors, techniques and technologies for radio frequency interference (RFI) identification and compensation, array optimization, and radio-wave adaptive optics. For future space missions, development should emphasize inexpensive large apertures, large-format arrays, receivers with the lowest possible noise, high-capacity, space-qualified refrigerators, and enhanced telemetry bandwidth. The panel supports the recommendation of the Panel on Ultraviolet, Optical, and Infrared Astronomy from Space that NASA pursue technology development leading toward a far-infrared (FIR)/submillimeter interferometer in space (see Chapter 7). The Single-Aperture Far Infrared (SAFIR) Observatory is the logical first step toward the long-term goal of space FIR/submillimeter interferometry, which could provide high-resolution imaging of star formation sites both locally and at high redshift. Such a capability will provide an excellent FIR/submillimeter complement to ALMA, EVLA, and SKA. The panel emphasizes that the National Science Foundation (NSF) has a special responsibility for radio astronomy, because it is primarily a ground-based activity. This responsibility is reflected in NSF’s current support for the university radio observatories as well as the national centers. The panel strongly endorses continuation of this support and recommends enhanced efforts to support full utilization of these essential facilities by their general users.

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Astronomy and Astrophysics in the New Millennium: Panel Reports The radio astronomy community is proud of the national radio astronomy centers. At centimeter wavelengths, the National Radio Astronomy Observatory (NRAO) and the National Astronomy and Ionosphere Center (NAIC) lead the world, and U.S. astronomers rely almost entirely on them for telescope access. The NSF needs to provide increased support to operate, maintain, and continually upgrade the radio facilities to keep them at the cutting edge, and it should seize the opportunity to develop subarcsecond imaging capabilities, complementing those of the VLA and the Next Generation Space Telescope (NGST) at shorter wavelengths (with ALMA) and at longer wavelengths (with LOFAR). The panel is concerned that NSF funding for critical activities such as data analysis, theory, correlative studies, and student support is not commensurate with its investment in facilities. The NSF should provide sufficient funds for individual investigators to maximize the scientific output of both national and university facilities. It should consider innovative ways to support astronomers in obtaining, analyzing, and publishing data, along with training a new generation of astronomers. This new support should complement the traditional grants program, for which the fraction of proposals that can be funded within the budget has fallen to dangerously low levels. The panel emphasizes that preservation of portions of the spectrum for future radio astronomical research is vital. The NSF plays a critical role in setting spectrum management policy and in increasing public awareness of its importance. Continued vigilance is required at both the national and international levels to ensure that spectrum allocation balances commercial and research interests. At the same time, investments must be made in the development of hardware and signal-processing techniques to mitigate the effects of human-generated radio interference, which will otherwise drown out the much weaker cosmic radio signals. In summary, technological advances in telescope hardware spanning the entire wavelength range of interest to radio and submillimeter astronomy now permit the construction of a new generation of powerful instruments. These powerful instruments will provide crucial information on the leading astronomical questions of the decade, especially on how the universe formed—from its superclusters, clusters, and galaxies to their constituent stars and planets. Full exploitation of these instruments will require adequate support for facilities and investigators and preservation of portions of the radio spectrum.

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Astronomy and Astrophysics in the New Millennium: Panel Reports SCIENCE OPPORTUNITIES Radio astronomy in the last decade has made fundamental contributions to the most important issues in astrophysics. By directly observing CMB radiation, radio astronomers have shown that its spectrum is described to remarkable accuracy by a thermal Planck spectrum, verifying the Big Bang model and illustrating beautifully the simple physics needed to describe the universe at only 2×10−5 times its present age. The present imaging of the weak anisotropy in the CMB indicates that the universe may be flat, a strong prediction of the inflationary theory. Ongoing observations of the CMB promise to constrain to high precision a host of parameters that describe our universe, including its curvature and, therefore, the energy density; the Hubble constant; the baryonic and dark matter content; and Einstein’s cosmological constant. High-resolution radio imaging allows the detailed measurement of the kinematics in galactic microquasars and their more powerful extragalactic counterparts and measurement of the speed of expansion of gamma-ray bursters. Such observations provide compelling evidence of a supermassive black hole in the heart of the nearby galaxy NGC 4258 and suggest the presence of many more massive black holes in galactic cores. In the past decade, radio astronomers have shown that most forming stars are surrounded by disks, and they have watched the expansion of material ejected from dying stars. Radar probes of Mercury have shown the existence of water ice in the polar craters of the planet closest to the Sun. Quite unexpectedly, it was the exquisitely precise timing of a pulsar spinning on its axis 161 times per second that led to the discovery by radio astronomers of the first extrasolar planetary system. In areas where radio astronomy is not the only channel of information, it provides a crucial complementary view. In nearly all forefront areas of astronomical research, from the solar neighborhood (star and planet formation) to the furthest reaches of the universe in space (high-redshift galaxies), time (the CMB), and energy (gamma-ray bursts), radio astronomy complements optical, infrared, ultraviolet, x-ray, and gamma-ray observations, delivering ever more detailed views of the cosmos. The imaging capabilities of the new arrays will produce fantastic and fascinating pictures of the otherwise invisible internal workings of molecular clouds producing planetary systems, of the active engines buried within the hearts of galaxies, and of the intricate wisps and filaments lacing the interstellar medium in the core of our galaxy, in the lobes of radio galaxy halos, and in the outermost reaches of distant clusters of galaxies. Fur-

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Astronomy and Astrophysics in the New Millennium: Panel Reports thermore, radio telescopes have already proven to be effective hunters of the faint ephemeral signatures of the titanic explosions signaling star deaths in the distant universe, as heralded by flashes of gamma rays. It is ever more clear that in the coming decades the diverse views provided by the whole of the electromagnetic spectrum will be synthesized into a coherent physics picture of the clockwork of the universe. The radio and submillimeter programs and facilities described in this chapter will be a vital part of this intellectual adventure. THE LARGE-SCALE STRUCTURE OF THE UNIVERSE Studies of the relic radiation of the Big Bang, the CMB, lie entirely within the province of radio astronomy. The CMB contains the fossil record of conditions existing in the very early universe before the time of recombination. The mapping of fluctuations in the brightness of the CMB—its anisotropy—provides a snapshot of conditions in the universe at a redshift z~1000, equivalent to an age of 300,000 years. The CMB contains the imprints of structures that later grew to produce the large-scale structure we see today. Studies of the CMB radiation and how it has propagated from the time of its generation to the current time of observation thus allow us to take inventory of the matter and energy content of our universe. A comprehensive program is under way to characterize the CMB anisotropy using ground-based (e.g., CBI, DASI, VSA, Viper, POLAR, Polatron), balloon-based (e.g., BOOMERANG, TopHat, BEAST, MAXIMA), and space-based (MAP, Planck) missions. The majority of these will be operational in the first few years of this decade, and their results will determine the specifications for the suite of missions to follow. As illustrated in Figure 4.1, observations of the details of the CMB will allow radio astronomers to directly test models of the emergence and evolution of large-scale structure, leading to the formation of the superclusters, clusters, and galaxies we see today. Before the end of the decade, radio astronomers will provide high-precision determinations of the primary cosmological parameters. Measurements of the polarization of the CMB will determine the contribution to CMB anisotropy from gravitational waves excited by the decaying inflationary potential in the early universe (t=10−30 s). Detection of the unique signature of gravitational waves on the CMB polarization will provide a measurement of the energy scale of the inflationary potential, on the order of 1016 GeV, well beyond the reach of particle

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Astronomy and Astrophysics in the New Millennium: Panel Reports FIGURE 4.1 Cosmology with the cosmic microwave background (CMB) radiation as promised by the planned ground-based (e.g., CBI, DASI, VSA, Viper, POLAR, and Polatron), balloon-based (e.g., BOOMERANG, TopHat, BEAST, and MAXIMA), and space-based (MAP, Planck) missions. The enlarged regions of the COBE CMB map of the whole sky show the vastly increased resolution expected from future experiments. The simulated high-resolution observations are shown for both a low-density “open” universe and a “flat” universe, which is favored by the inflationary theory for the origin of the universe. The slight variations in the intensity of the CMB measure the inhomogeneities in the universe 300,000 years after the Big Bang. These inhomogeneities eventually grew into the rich structure observed today, as seen, for example, in the HST image shown bottom right. The most efficient way of extracting the cosmological information from CMB maps is to look at the amplitude of temperature fluctuations at different angular scales. This power spectrum is indicated bottom left for today’s experiments and top right for the level of accuracy expected within the next 10 years. The two curves shown are for open and flat cosmological models—whether current models are correct and whether the universe is open or flat will be easy to tell. The combination of results promised for the next decade will determine the correct cosmological model for our universe and measure its parameters with high precision. Courtesy of J.Carlstrom, University of Chicago, D.Scott, University of British Columbia, and M.White, Harvard-Smithsonian Center for Astrophysics.

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Astronomy and Astrophysics in the New Millennium: Panel Reports accelerators and with a sensitivity to the gravity-wave background well beyond that possible with direct gravity-wave detectors. Such scales are of great interest not only to cosmologists but also to particle physicists working on constructing a fundamental “theory of everything.” Polarization measurements will be difficult and will require, depending on just what the universe is up to, a combination of ground- and space-based instruments toward the end of this decade and beyond, but the importance of these measurements is tremendous. In the end, the observations made by these instruments will tell us whether the inflationary model for the origin of the Big Bang is correct or whether our understanding of the origin of the universe must undergo another major revision. The small distortion of the background radiation induced when CMB photons scatter off electrons in the hot gas contained within clusters of galaxies is known as the Sunyaev-Zel’dovich (SZ) effect. On its own, the SZ effect is an effective probe of the baryon density in the cluster intergalactic medium. In concert with x-ray observations of free-free emission from the same gas, the SZ effect provides an independent determination of the Hubble constant from local as well as high-redshift clusters. Figure 4.2 illustrates the promise of SZ mapping for tracking the census of galaxy

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Astronomy and Astrophysics in the New Millennium: Panel Reports clusters through time, thus strongly constraining models of structure formation. The second-order SZ effect, due to the CMB dipole that the cluster itself sees, can also provide a measurement of the peculiar velocity in its own frame of rest (i.e., the kinematic SZ effect). The smallest antennas proposed for CARMA will be critical for conducting large-scale SZ surveys of the high-redshift universe, while submillimeter observations with the SPST will measure the spectral dependence of the SZ effect. The large collecting area and high spatial resolution provided by ALMA at 7- to 10-mm wavelengths will allow sensitive detailed imaging of the SZ effect from distant clusters. Radio astronomy also provides its own direct probes of the expansion history of the universe and the allowed values of the cosmological FIGURE 4.2 Montage of observations and simulations of the Sunyaev-Zel’dovich (SZ) effect. The top montage shows SZ effect images, obtained using dedicated centimeter-wave receivers on the OVRO and BIMA millimeter-wave arrays, of three galaxy clusters at redshifts z=0.17, z=0.54, and z=0.83 (at z=0.83, the universe is approximately one-third of its present age). The same contour level is used for each SZ image. Insets show x-ray images of each cluster, with the same intensity scale used for each cluster. The signature of the SZ effect is comparable at all three distances, whereas the detected x-ray emission (in fact, any emission) decreases rapidly with distance. Hence SZ effect observations allow detection of clusters throughout the observable universe. As illustrated in the bottom left panel, observations of the abundance of clusters at different redshifts, corresponding to different epochs, will allow discriminating between cosmological models. The inset shows the limiting cluster mass Mlim as a function of redshift for a realistic SZ effect survey instrument. The bottom right panel illustrates the expected image of the SZ effect for a simulated supercluster (by D.Bond, Canadian Institute of Theoretical Astrophysics). Future very sensitive SZ observations promise to image the intercluster gas (green and blue in the image), a diffuse cosmic web that is likely to be the largest reservoir of baryons or normal matter in the universe. CARMA, ALMA, and SPST will provide the range of sensitivity, resolution, stability, and sky coverage needed to exploit all aspects of the SZ effect for cosmology. Courtesy of J.Carlstrom and J.Mohr, University of Chicago.

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Astronomy and Astrophysics in the New Millennium: Panel Reports constant. Gravitational lensing, in particular that due to individual galaxies, which causes image splitting on scales of arcseconds, gives measurements of the Hubble constant through time-delay observations. Additionally, the gravitational mass, luminous plus dark matter, in the lensing galaxy is measured. Ongoing and future large surveys of lensing in samples of compact radio galaxies and quasars will determine parameters such as the cosmological constant, matter density, and curvature. In addition to providing large lens samples, the EVLA will offer great improvements in the ability to monitor lens systems for time-delay measurements. The order-of-magnitude increase in sensitivity promised by the future SKA will likewise offer a leap forward in lens statistics. Radio-source surveys provide the bread-and-butter source count statistics, object identifications, and parent samples that enable high-profile cosmological studies. In particular, gravitational-lens surveys are possible only after a catalog of target sources is available. Furthermore, an understanding of lens statistics requires knowledge of the radio-luminosity relationship as a function of redshift. Other radio-source-based cosmological tests are important: angular size versus redshift, superluminal jet speed versus redshift, and geometric distance measurements made by observing maser hot spots and supernova expansion. Additionally, CMB studies must be carefully corrected for foreground

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Astronomy and Astrophysics in the New Millennium: Panel Reports and remote operation. At the longest wavelengths, LOFAR will have about a million square meters of collecting area—equivalent to that of the SKA. COSMIC MICROWAVE BACKGROUND EXPERIMENTS Because of the large number of imminent observations and the likelihood of surprises, the panel elects not to specify in detail future CMB missions and projects. Clearly, however, further study of the CMB radiation will produce unique and fundamental clues to the processes and evolution of the earliest epochs. In particular, the panel recommends the following: Continued support of the ambitious suite of ground-based and balloon-borne experiments, satellite missions, and extensive theoretical studies of the CMB radiation that will allow direct determination of the fundamental parameters that govern the cosmology describing the origin and evolution of our universe. The program will culminate with the completion of the MAP and Planck space missions during this decade. The construction of dedicated instruments to carry out large-scale imaging surveys and high-sensitivity spectral observations of the SZ effect in order to obtain a redshift-independent inventory of the cosmic web of large-scale structure, to determine the expansion history of the universe, and to measure the velocities of massive galaxy clusters and superclusters relative to the Hubble flow. The establishment of small exploratory programs to investigate and develop the techniques and technology for extracting the detailed polarization structure of the CMB that will directly test the ingredients of the inflationary model for cosmology. The results of these efforts will guide planning for the Planck mission and also set the stage for post-Planck mission planning in the CMB field. FAR-INFRARED/SUBMILLIMETER INTERFEROMETER IN SPACE The far-infrared/submillimeter spectral region contains about half the luminosity of the universe and carries vital diagnostics for galaxy, star, and planet formation. An integral part of the radio/submillimeter vision is thus the development of a capability for FIR/submillimeter interferometry in space. As can be seen plainly in Figure 4.11, a FIR space interferometer will fill a crucial gap between NGST and ALMA in the wavelength-

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Astronomy and Astrophysics in the New Millennium: Panel Reports resolution plane. The science addressed by such an instrument requires superb sensitivity in continuum and high-spectral-resolution modes (λ/Δλ≥105). During this decade, technology development and precursor missions are needed. LABORATORY ASTROPHYSICS Laboratory studies underpin the interpretation of astronomical observations at all wavelengths. This is particularly true as new spectral windows such as the submillimeter and far infrared are exploited. Support for laboratory astrophysics is becoming increasingly difficult to obtain and must be enhanced to meet the scientific objectives of the existing and planned radio and submillimeter facilities. Relevant laboratory measurements are an integral component of the analysis of astronomical data, and funds for such research should be included in both NASA- and NSF-supported astronomy programs. SOLAR RADIO ASTRONOMY Observations of the Sun at radio wavelengths contribute significantly to the study of transient energetic phenomena, the nature and evolution of coronal magnetic fields, and the solar atmosphere. A suitable dedicated instrument such as the proposed Frequency Agile Solar Radio telescope (FASR) discussed by the Panel on Solar Astronomy appears to be feasible and would be ideal for the continued investigation of these areas. While it is possible that some of the objectives of FASR, particularly studies of transient phenomena, might be met by modifying current or planned instruments such as the 1HT, the EVLA, and LOFAR, the panel recognizes the importance of constructing a facility dedicated to the study of the Sun. TECHNOLOGY FOR THE FUTURE The coming decades promise truly remarkable developments in radio and submillimeter astronomy. Projects under way or just beginning (ALMA, SMA, SOFIA, and FIRST/Planck) will improve the sensitivity resolution product of submillimeter observations by one to two orders of magnitude. Projects on the 2010 horizon (SKA, a FIR/submillimeter interferometer in space, and space-based CMB polarization observations)

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Astronomy and Astrophysics in the New Millennium: Panel Reports will push the sensitivity×resolution product orders of magnitude further. To achieve these ambitious goals, technology development must be pursued aggressively throughout the chain, from telescope to detector to processing electronics and data reduction/image processing. As the pace of technological innovation quickens, it is essential to pursue a technology development strategy that maintains the health of a range of different institutions and approaches, rewards innovation, and maintains a base of talented researchers well connected to the science of the field. To this end, the panel recommends emphasizing a number of areas, which have been classified as ground-based or space-based. GROUND-BASED NEEDS AND OPPORTUNITIES The large arrays that are under development rely on very wide receiver bandwidths to improve their sensitivity and on a large number of elements to generate high-fidelity images. The resulting downstream processing must deal with bandwidths greater than 1 Tbps, which places severe demands on correlator technology. While the rapid pace of semiconductor innovation will help, it is likely that novel approaches to megacorrelator design will be needed. The wide bandwidths also lead to dramatically increased sensitivity to radio-frequency interference (RFI). With the advent of high-redshift astronomy, astronomical research must extend beyond the small, protected frequency windows established for radio astronomy into spectral ranges (necessarily) allocated for commercial and other purposes. Radio astronomers, accordingly, must develop ways to characterize and excise man-made signals in order to recognize and study cosmic ones. It will thus be imperative to characterize and excise interference where and when it occurs. Eventually, it should be possible to construct the entire receiver/intermediate-frequency (IF) chain after the mixer in digital circuitry at radio frequencies, opening up a wealth of new possibilities. At their largest extents, ground-based arrays suffer from atmospheric or ionospheric phase distortion, and phase-correction schemes (the radio equivalent of adaptive optics) must be further developed. Finally, large-scale surveys for a wide variety of objects would most profitably be carried out by large detector arrays at single-dish instruments, as would spectral line imaging with large-format, heterodyne receiver (SIS) arrays.

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Astronomy and Astrophysics in the New Millennium: Panel Reports SPACE-BASED NEEDS AND OPPORTUNITIES The extraordinarily low natural backgrounds at radio and submillimeter wavelengths lead to superb sensitivities for space-based telescopes. To take advantage of this sensitivity, a new generation of large-format, incoherent arrays is needed. Bolometer development must be continued, as must the design of superconducting detectors that can also be used as energy-resolved photon counters in the optical and UV. A major stumbling block at present is the design of multiplexers for large-format arrays. The telescopes as well as the detectors must be kept at very low temperatures, so the development of high-capacity, space-qualified refrigerators must be accelerated. In certain cases (e.g., spectral line work), heterodyne receivers may provide alternatives to direct detectors provided they operate at or near their quantum noise limit. As detectors and processing electronics approach their fundamental sensitivity limits, the only means left for improving sensitivity is to increase the collecting area. Large, inexpensive apertures, including inflatable ones, are therefore another high-priority item for space-based radio and submillimeter astronomy. Finally, instruments with large numbers of detectors or imaging elements produce data streams that cannot be dealt with using existing downlinks, and new means must be found to increase the telemetry bandwidth for future missions (true for all wavelengths). POLICY ISSUES OPEN SKIES POLICY The panel reaffirms that the open skies policy—allocating telescope time based purely on scientific merit—is the policy that enables the best science to be undertaken. However, the panel is concerned about how future cost-sharing arrangements may affect this policy. Traditionally, some foreign radio facilities have provided comparable open access. The panel encourages continued dialogue to enable U.S. astronomers to have open access to all facilities, particularly those operating at millimeter wavelengths.

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Astronomy and Astrophysics in the New Millennium: Panel Reports RADIO SPECTRUM MANAGEMENT Radio-frequency interference is a worldwide problem that transcends national boundaries and policies. For decades, U.S. radio astronomers have been active in the spectrum management activities of the International Astronomical Union (IAU), the International Union of Radio Science (URSI), and the International Telecommunication Union (ITU). Radio astronomers from around the world have collaborated closely to preserve their common interests in the face of powerful commercial, government, and military interests. The recent award-winning film produced by NSF on the need for preservation of the radio spectrum is an outstanding example of NSF’s proactive effort in this arena. The panel recommends continued U.S. participation and vigorous involvement in spectrum management issues. THE NATIONAL RADIO ASTRONOMY OBSERVATORY AND THE ATACAMA LARGE MILLIMETER ARRAY It is imperative that the United States maintain its leadership and critical involvement in ALMA. Given the demonstrated effectiveness of the NRAO organization, the panel urges that to operate ALMA, no new institution be created as an entity separate from NRAO. At the same time, NRAO’s other unique and vital facilities must be run in synergy with ALMA, not in competition with it. AGENCY FUNDING AND MANAGEMENT POLICIES The NSF needs to provide adequate support for operating, maintaining, and continually upgrading federally funded radio facilities (both the national centers and the university radio facilities) to keep them at the cutting edge. Increased and continuing investment is needed. The NSF’s funding for ancillary activities such as observing preparation, data analysis, theory, and correlative studies is not commensurate with its investment in facilities. The NSF should provide sufficient funds to allow individual investigators to maximize the scientific output of the facilities it supports. In particular, NSF should plan to make available sufficient funds for data reduction and analysis as well as for the maintenance and operation of the new facilities. The panel endorses the recommendations laid out in

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Astronomy and Astrophysics in the New Millennium: Panel Reports the survey committee report with regard to the funding of new programs and facilities. The NSF should also establish a national postdoctoral program similar to the Hubble Fellowship program that includes support for outstanding young scientists pursuing research associated with the NSF-supported radio facilities. Making the provision of leveraged or matching funds a criterion for grant support may in some cases compromise the opportunity to pursue individual initiatives. The NSF should examine the circumstances under which such support is required and should ensure that review panels do not give undue weight to the availability of matching funds in programs that do not require them. ACKNOWLEDGMENTS The panel benefited from written comments received from many individuals through the American Astronomical Society (AAS) discussion forum and oral comments at the public forums conducted during the AAS meetings in January and June 1999 and at the URSI meeting in January 1999. Presentations to the panel were made by J.Baars (University of Massachusetts), D.Backer (University of California at Berkeley), F.Bash (University of Texas), T.Bastian (NRAO), L.Blitz (University of California at Berkeley), R.Brown (NRAO), M.Davis (NAIC), R.Dickman (NSF), D.Gary (New Jersey Institute of Technology), R.Ekers (Australia Telescope National Facility), P.Goldsmith (NAIC), N.Kassim (Naval Research Laboratory), T.J.Lazio (Naval Research Laboratory), D.Leisawitz (NASA), J.Mather (NASA), H.Moseley (NASA), R.Perley (NRAO), J.Peterson (Carnegie Mellon University), P.Schloerb (University of Massachusetts), A.Stark (Harvard-Smithsonian Center for Astrophysics), R.Taylor (University of Calgary), H.Thronson (NASA), M.Turner (University of Chicago), J.Ulvestad (NRAO), P.Vanden Bout (NRAO), K.Weiler (Naval Research Laboratory), and D.Woody (California Institute of Technology). ACRONYMS AND ABBREVIATIONS 1HT —One Hectare Telescope AAS —American Astronomical Society

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Astronomy and Astrophysics in the New Millennium: Panel Reports AGN —active galactic nuclei ALMA —Atacama Large Millimeter Array ARISE —Advanced Radio Interferometry between Space and Earth, an orbiting antenna that will be used in concert with the ground-based VLBA AU —astronomical unit. A basic unit of distance equal to the separation between Earth and the Sun, about 150 million km BEAST —Background-Emission-Anisotropy Scanning Telescope; a long-duration, balloon-borne cosmic microwave background experiment BIMA Array —Berkeley-Illinois-Maryland Association Array BOOMERANG —Balloon Observations of Millimetric Extragalactic Radiation and Geophysics; a balloon-borne telescope that circumnavigated Antarctica CARMA —Combined Array for Research in Millimeter-wave Astronomy, a millimeter-wave array in the Northern Hemisphere CBI —Cosmic Background Imager, a 13-element interferometer located in northern Chile CMB —cosmic microwave background CMVA —Coordinated Millimeter VLBI Array COBE —Cosmic Background Explorer, a NASA mission launched in 1989 to study the cosmic background radiation from the Big Bang CSO —Caltech Submillimeter Observatory, a 10-m telescope operating on Mauna Kea, Hawaii, used for observations of millimeter and submillimeter wavelength radiation D/H —deuterium/hydrogen ratio DASI —Degree-Angular-Scale Interferometer for imaging anisotropy in the cosmic microwave background EVLA —Expanded Very Large Array FASR —Frequency-Agile Solar Radio telescope FCRAO —Five College Radio Astronomy Observatory FIR —far infrared FIRST —European Far Infrared Space Telescope GBT —Green Bank Telescope GRB —gamma-ray burst HALCA —Highly Advanced Laboratory for Communications and Astronomy, the Japanese VSOP satellite launched in February of 1997 HI —atomic hydrogen HII —ionized hydrogen

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Astronomy and Astrophysics in the New Millennium: Panel Reports HST —Hubble Space Telescope, a 2.4-m-diameter space telescope designed to study visible, ultraviolet, and infrared radiation, and the first of NASA’s Great Observatories IAU —International Astronomical Union IMF —initial mass function IR —infrared IRAS —Infrared Astronomical Satellite, a NASA Explorer satellite launched in 1983 that surveyed the entire sky in four infrared wavelength bands using a helium-cooled telescope ISM —interstellar medium ITU —International Telecommunication Union JPL —Jet Propulsion Laboratory (NASA) KBO —Kuiper Belt object LMT —Large Millimeter Telescope LOFAR —Low Frequency Array, a joint Dutch-U.S. initiative to make observations at radio wavelengths longer than 2 m MAP —Microwave Anisotropy Probe mission MAXIMA —Millimeter Anisotropy Experiment Imaging Array; a balloon-borne millimeter-wave telescope designed to measure the cosmic microwave background NAIC —National Astronomy and Ionosphere Center, Arecibo, Puerto Rico NASA —National Aeronautics and Space Administration NFRA —Netherlands Foundation for Research in Astronomy NGST —Next Generation Space Telescope, an 8-m infrared space telescope NICMOS —Near Infrared Camera and Multi-Object Spectrometer, an instrument on the Hubble Space Telescope NRAO —National Radio Astronomy Observatory NRL —Naval Research Laboratory NSF —National Science Foundation NVSS —NRAO VLA Sky Survey OVRO —Owens Valley Radio Observatory POLAR —Polarization Observations of Large Angular Regions, an instrument designed to measure the polarization of the cosmic microwave background Planck Surveyor —A European-led space mission to image anisotropies in the CMB. Polatron —a bolometric receiver with polarization capability designed for use at the Owens Valley 5.5-m radio telescope

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Astronomy and Astrophysics in the New Millennium: Panel Reports RADIOASTRON —A Russian satellite designed to conduct VLBI observations of radio sources in conjunction with the global ground VLBI network RFI —radio-frequency interference SAFIR —Single Aperture Far Infrared Observatory SCUBA —Submillimeter Common-User Bolometer Array, a British-French-Canadian ground-based telescope located in Hawaii; it operates at wavelengths between 350 and 2000 µm. SIRTF —Space Infrared Telescope Facility, NASA’s fourth Great Observatory, will study infrared radiation SIS heterodyne receivers —devices that use a SIS superconducting junction, a junction consisting of two layers of superconducting metal (niobium) separated by a few nanometers of insulator (aluminum oxide) SKA —Square Kilometer Array, an international centimeter-wave radio telescope SMA —Submillimeter Array SOFIA —Stratospheric Observatory for Infrared Astronomy, a 2.5-m telescope flown above most of the Earth’s water vapor in a modified Boeing 747 aircraft to study infrared and Submillimeter radiation SPST —South Pole Submillimeter Telescope STScI —Space Telescope Science Institute SZ effect —Sunyaev-Zel’dovich effect, the small distortion of the CMB radiation induced when CMB photons scatter off electrons in the hot gas contained within clusters of galaxies TopHat —A NASA-sponsored experiment in which a telescope was placed on top of a balloon to measure cosmic microwave background radiation anisotropy ULIRG —ultraluminous infrared galaxy URSI —International Union of Radio Science Viper —A 2-m telescope designed to measure anisotropy in the CMB at angular scales down to 0.1 deg VLA —Very Large Array, a radio interferometer in New Mexico consisting of 27 antennae spread out over 35 km and operating with 0.1-arcsec resolution VLBA —Very Long Baseline Array, an array of radio telescopes operating as an interferometer with a transcontinental baseline and resolution less than a thousandth of an arcsecond VLBI —Very Long Baseline Interferometry, a technique whereby a network of radio telescopes can operate as an interferometer.

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Astronomy and Astrophysics in the New Millennium: Panel Reports VSA —Very Small Array, a project to make images of the CMB radiation on angular scales of around 1 deg VSOP —VLBI Space Observatory Program, a mission led by the Institute of Space and Astronautical Science in collaboration with the National Astronomical Observatory of Japan WFPC —Wide-Field Planetary Camera, an instrument on the Hubble Space Telescope

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