Pathways to Discovery in Astronomy and Astrophysics for the 2020s (2023) / Chapter Skim
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Appendix M: Report of the Panel on Radio, Millimeter, and Submillimeter Observations from the Ground
Appendix M: Report of the Panel on Radio, Millimeter, and Submillimeter Observations from the Ground
Pages 472-497
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From page 472... ...
. This record encompasses discoveries made by two types of RMS facilities: experiments, which are designed, built, and used by dedicated teams to address focused sets of science questions, and observatories, which offer diverse and flexible sets of observational capabilities to broad communities of astronomers and can therefore address wide ranges of science questions.
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From page 473... ...
Listed in order of nearest to most distant observational target(s) , these are: ° Broadband, high-cadence, spectropolarimetric imaging of the Sun to trace flares, shocks, and coronal mass ejections and to understand the drivers of space weather; ° High-resolution imaging of jets driven by supermassive black holes in the centers of galaxies to determine how such jets are launched and powered; ° Surveying the static and time-variable radio sky with an innovative new "radio camera" to address a wealth of science questions using statistical samples of star-forming galaxies and fast radio bursts; and ° Mapping the evolution of neutral atomic hydrogen (HI)
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From page 474... ...
producing exquisitely sharp images of galaxies, black holes, and protoplanetary disks. RMS detectors on these telescopes can distinguish the signatures of specific atoms and molecules from those of thermal plasmas that glow because they are warm, and in turn from the nonthermal emission produced by charged particles accelerating in strong magnetic fields.
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From page 475... ...
ALMA spectral line observations have revealed the kinematics of disks around forming stars and black holes, thereby enabling measurements of their masses, and have probed the gas mass reservoirs in high-redshift galaxies, revealing the factors that drive the cosmic star formation history. Detailed images of gravitationally lensed galaxies have demonstrated the potential to detect and measure the masses of dark matter subhalos, while closer to home, spectacular ALMA images of the solar chromosphere have provided essential data for studying the outer layers of the Sun.
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(c) Image of the supermassive black hole at the center of the galaxy M87, obtained by the Event Horizon Telescope observatories in conjunction with ALMA (Event Horizon Telescope Collaboration et al., 2019)
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From page 477... ...
Foremost among these was an impressive suite of white papers -- innovative, ambitious, and wide-ranging -- that laid out projects and priorities for the next 10 years and beyond. In reviewing these white papers and engaging with the teams who submitted them, the panel was guided by the high-priority science questions and discovery areas identified by the six Astro2020 science panels.
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From page 478... ...
within the RMS portfolio. TABLE M.1 High-Priority Science Questions Versus RMS Facilities CMB-S4 Arecibo ngVLA MSO1 MSO2 MSO3 MSO4 ALMA VLBA GBT VLA Science Frontier Panel Questions/Discovery Areas Panel on the Interstellar Medium and Star and Planet Formation (ISM)
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3. How do supermassive black holes form and how is their growth coupled to the evolution of their host galaxies?
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that are broadly aligned with the Astro2020 high-priority science questions. This section highlights areas in which the ngVLA's capabilities would allow it to make extraordinary contributions to addressing those questions, grouped by the RMS panel according to three broad science themes.
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The ngVLA's combination of high spatial resolution and centimeter-wavelength continuum sensitivity would resolve protoplanetary disks on scales more than 20 times finer than ALMA, potentially capturing images of planet formation in action as young planets clear gaps in the disk. The inner regions of these disks, within a few astronomical units of the central star, are often too opaque to be studied at the shorter ALMA wavelengths.
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At lower masses, spectacular gravitational wave detections have revealed the mergers of individual stellar-mass black holes forming more massive black holes, yet the extent of a population of intermediate-mass black holes, between the extremes of SMBHs and stellar-mass black holes, remains uncertain, and questions remain concerning the masses and spins of binary black holes prior to merger and how those properties map to stellar progenitors. This subsection highlights how the ngVLA would address key open questions on black holes and galaxies as identified by the COEP and GAL science panels.
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These brief, energetic events can trace stellar deaths, which drive the chemical enrichment of their surroundings and lead to the formation of neutron stars and black holes. Signatures of the binary neutron star merger GW170817 were detected across the electromagnetic spectrum after the initial gravitational wave signature of coalescence, beginning with the burst of gamma rays 2 seconds later, followed by an optical counterpart within 11 hours -- and a VLA radio detection of an emerging relativistic jet 16 days after the detection of gravitational waves.
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to large, predefined surveys. M.3.4 Cost, Schedule, and Risks The ngVLA project team has prepared a detailed project design, plan, schedule, and cost model.
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M.3.5 Additional Programmatic Guidance The RMS panel views the ngVLA as an exciting concept for a flexible, powerful, PI-driven observatory that would address a wide range of Astro2020 high-priority science questions. In support of the project's long-term success, the RMS panel offers three suggestions for its implementation.
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and international cosmology communities to address four science themes. The following subsections connect its capabilities to the science questions identified by the Astro2020 science panels.
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CMB measurements already demonstrate the reality of the cosmic neutrino background predicted by Big Bang cosmology despite the absence of laboratory detections. To accomplish these goals, CMB-S4 is designed with the angular resolution, sensitivity, and sky coverage needed to precisely measure the perturbations caused by relativistic particles that decouple from the hot early universe within the first nanosecond (COS-2b)
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The scattering of CMB photons by hot electrons results in a characteristic CMB spectral distortion, known as the thermal SZ effect, with an amplitude proportional to the integrated pressure of the hot gas. While this technique has seen its greatest use for the detection and characterization of galaxy clusters, the sensitivity and sky coverage of CMB-S4 maps would make it possible to explore the ionized gas of the circumgalactic medium (GAL-D)
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M.4.5 Additional Programmatic Guidance The RMS panel views CMB-S4 as a powerful, cosmology-focused experiment that would address Astro2020 priority science questions at a level that no other concepts can. In support of the project's longterm success, the RMS panel offers the following two suggestions for its implementation.
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From page 490... ...
In particular, based on the Astro2020 high-priority science questions, the RMS panel has identified four areas in which outstanding scientific opportunities exist for new mid-scale RMS facilities. These areas are discussed in detail below, with reference to the specific white papers that inspired them, although because each still requires navigating a complex path to a successfully competed MSRI-2 (up to $70 million)
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A second key area of mid-scale opportunity is high-resolution imaging of jets driven by supermassive black holes in the centers of galaxies. The current state of the art in terms of resolution is provided by the EHT, an experiment that has regularly combined a number of telescopes around the world (including ALMA)
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would enable studies of jet physics on scales farther from the Schwarzschild radius, and through the EHT's ability to resolve binary black holes at high angular resolution would also help address the question of how supermassive black holes grow (COEP-4, GAL-3)
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Possible architectures could include an "EoR imager" focused on cross-correlations with multi-wavelength probes of structure at redshifts z <12, and a "Cosmic Dawn Array" focused on z >12 power spectrum measurements where non-HI probes are unavailable. Connections to high-priority science questions are clear: characterization of HI in the early universe would directly constrain the thermal history of the intergalactic medium and the topology of reionization (GAL-1)
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RMS facilities. From the Astro2020 science panel reports, it is clear that pulsar timing capabilities are critical for tackling a number of high-priority science questions: the mass and spin distributions for neutron stars and black holes (COEP-1)
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Taylor, 2019, "Spectrum Management," white paper submitted to Astro2020: Decadal Survey on Astronomy and Astrophysics, https://baas. aas.org/pub/2020n7i136/release/1.
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As discussed above (and reflected in Table M.1) , ALMA is a productive and scientifically vibrant observatory, which has already engaged an impressively broad swath of the global astronomical community and is poised to make further progress on many of the next decade's high-priority science questions.
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From page 497... ...
To make sure that telescope sites are ultimately returned to their original conditions, projects need to understand and budget for all decommissioning activities before receiving construction funding. To help ensure that RMS facilities' impacts are as positive for their immediate communities as for society at large, the panel suggests that agencies provide funding for meaningful stakeholder engagement at all phases of the project life cycle.
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