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Register a new userScience with an ngVLA: The ngVLA Science Case and Associated Science Requirements
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The science case and associated science requirements for a next-generation Very Large Array (ngVLA) are described, highlighting the five key science goals developed out of a community-driven vision of the highest scientific priorities in the next decade. Building on the superb cm observing conditions and existing infrastructure of the VLA site in the U.S. Southwest, the ngVLA is envisaged to be an interferometric array with more than 10 times the sensitivity and spatial resolution of the current VLA and ALMA, operating at frequencies spanning $sim1.2 - 116$,GHz with extended baselines reaching across North America. The ngVLA will be optimized for observations at wavelengths between the exquisite performance of ALMA at submm wavelengths, and the future SKA-1 at decimeter to meter wavelengths, thus lending itself to be highly complementary with these facilities. The ngVLA will be the only facility in the world that can tackle a broad range of outstanding scientific questions in modern astronomy by simultaneously delivering the capability to: (1) unveil the formation of Solar System analogues; (2) probe the initial conditions for planetary systems and life with astrochemistry; (3) characterize the assembly, structure, and evolution of galaxies from the first billion years to the present; (4) use pulsars in the Galactic center as fundamental tests of gravity; and (5) understand the formation and evolution of stellar and supermassive blackholes in the era of multi-messenger astronomy.
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The next-generation Very Large Array (ngVLA) is an astronomical observatory planned to operate at centimeter wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 to 116 GHz). The observatory will be a synthesis radio telescope constituted of approximately 244 reflector antennas each of 18 meters diameter, and 19 reflector antennas each of 6 meters diameter, operating in a phased or interferometric mode. We provide a technical overview of the Reference Design of the ngVLA. This Reference Design forms a baseline for a technical readiness assessment and the construction and operations cost estimate of the ngVLA. The concepts for major system elements such as the antenna, receiving electronics, and central signal processing are presented.
Observations with modern radio telescopes have revealed that classical novae are far from the simple, spherically symmetric events they were once assumed to be. It is now understood that novae provide excellent laboratories to study several astrophysical properties including binary interactions, stellar outflows, and shock physics. The ngVLA will provide unprecedented opportunities to study these events. It will enable us to observe more distant and fainter novae than we can today. It will allow us to simultaneously resolve both the thermal and non-thermal components in the ejecta. Finally, monitoring novae with the ngVLA will reveal the evolution of the ejecta in better detail than is possible with any current instrument.
Extraterrestrial amino acids, the chemical building blocks of the biopolymers that comprise life as we know it on Earth are present in meteoritic samples. More recently, glycine (NH$_2$CH$_2$COOH), the simplest amino acid, was detected by the Rosetta mission in comet 67P. Despite these exciting discoveries, our understanding of the chemical and physical pathways to the formation of (pre)biotic molecules is woefully incomplete. This is largely because our knowledge of chemical inventories during the different stages of star and planet formation is incomplete. It is therefore imperative to solidify our accounting of the chemical inventories, especially of critical yet low-abundance species, in key regions and to use this knowledge to inform, expand, and constrain chemical models of these reactions. This is followed naturally by a requirement to understand the spatial distribution and temporal evolution of this inventory. Here, we briefly outline a handful of particularly-impactful use cases in which the ngVLA will drive the field forward.
This chapter reviews some of the expected contributions of the ngVLA to the understanding of the late evolutionary stages of low-to-intermediate mass stars, including asymptotic giant branch (AGB) stars, post-AGB stars, and pre-planetary nebulae. Such objects represent the ultimate fate of stars like the Sun, and the stellar matter they lose to their immediate vicinity contributes significantly to the chemical enrichment of galaxies. Topics addressed in this chapter include continuum imaging of radio photospheres, studies of circumstellar envelopes in both thermal and nonthermal lines, and the investigation of the transition stages from the AGB to planetary nebulae using radio wavelength diagnostics. The authors gratefully acknowledge contributions to the content of this chapter from members of the evolved star community.
Planets assemble in the midplanes of protoplanetary disks. The compositions of dust and gas in the disk midplane region determine the compositions of nascent planets, including their chemical hospitality to life. In this context, the distributions of volatile organic material across the planet and comet forming zones is of special interest. These are difficult to access in the disk midplane at IR and even millimeter wavelengths due to dust opacity, which can veil the midplane, low intrinsic molecular abundances due to efficient freeze-out, and, in the case of mid-sized organics, a mismatch between expected excitation temperatures and accessible line upper energy levels. At ngVLA wavelengths, the dust is optically thin, enabling observations into the planet forming disk midplane. ngVLA also has the requisite sensitivity. Using TW Hya as a case study, we show that ngVLA will be able to map out the distributions of diagnostic organics, such as CH3CN, in nearby protoplanetary disks.
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