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Register a new userScience with an ngVLA: Accreting Supermassive Black Holes in Nearby Low-mass Galaxies
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The ngVLA will facilitate deep surveys capable of detecting the faint and compact signatures of accreting supermassive black holes (SMBHs) with masses below one million solar-masses hosted by low-mass ($< 10^9$ solar-masses) galaxies. This will provide important new insights on both the origins of supermassive black holes and the possible impact of active galactic nucleus-driven feedback in a currently unexplored mass regime.
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Emission line observations of circumnuclear gas disks in the ALMA era have begun to resolve molecular gas tracer kinematics near supermassive black holes (BHs), enabling highly precise mass determination in the best cases. The ngVLA is capable of extremely high spatial resolution imaging of the CO(1-0) transition at 115 GHz for nearby galaxies. Furthermore, its high (anticipated) emission line sensitivity suggests this array can produce benchmark BH mass measurements. We discuss lessons learned from gas-dynamical modeling of recent ALMA data sets and also compare ALMA and ngVLA CO simulations of a dynamically cold disk. While only a fraction of all local galaxies likely possess sufficiently bright, regularly-rotating nuclear molecular gas, in such cases the ngVLA is expected to more efficiently resolve such emission arising at a projected 50-100 mas from the central BH.
Stars form in cold clouds of predominantly molecular (H2) gas. We are just beginning to understand how the formation, properties, and destruction of these clouds varies across the universe. In this chapter, we describe how the thermal line imaging capabilities of the proposed next generation Very Large Array (ngVLA) could make major contributions to this field. Looking at CO emission, the proposed ngVLA would be able to quickly survey the bulk properties of molecular clouds across the whole nearby galaxy population. This includes many unique very nearby northern targets (e.g., Andromeda) inaccessible to ALMA. Such surveys offer a main observational constraint on the formation, destruction, lifetime, and star formation properties of clouds. Targeting specific regions, the ngVLA will also be able to heavily resolve clouds in the nearest galaxies. This will allow detailed studies of the substructure and kinematics --- and so the internal physics --- of clouds across different chemical and dynamical environments.
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.
We demonstrate the feasibility of uncovering supermassive black holes in late-type, quiescent spiral galaxies by detecting signs of very low-level nuclear activity. We use a combination of x-ray selection and multi-wavelength follow-up. Here, we apply this technique to NGC 3184 and NGC 5457, both of type Scd, and show that strong arguments can be made that both host AGNs.
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.
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