Science with an ngVLA: Neutral Atomic Hydrogen in the Local Universe

TL;DR

The paper discusses how the ngVLA will revolutionize our understanding of atomic hydrogen gas in the local universe, shedding light on galaxy gas flows, star formation, and the transition from atomic to molecular gas.

Contribution

It highlights the capabilities of the ngVLA in measuring HI content, resolving HI clouds, and providing absorption spectra, advancing studies of galaxy evolution and star formation.

Findings

ngVLA will measure sizes of HI disks around galaxies.

It will resolve HI clouds in numerous galaxies beyond the Local Group.

Provides dense HI absorption spectra in the Milky Way.

Abstract

One of the outstanding questions in astronomy today is how gas flows from the circumgalactic medium (CGM) onto the disks of galaxies and then transitions from the diffuse atomic medium into molecular star-forming cores. For studies of the CGM, the Next Generation Very Large Array (ngVLA) will have the sensitivity and resolution to measure the sizes of the neutral atomic hydrogen (HI) disks of galaxies and complete a census of the HI content around galaxies. Within galaxies, the ngVLA will be able to resolve HI clouds in large numbers of galaxies beyond the Local Group providing measurements of the physical conditions of gas across a wide range of galaxy types. Finally, within our own Milky Way, the ngVLA will provide a dense grid of HI absorption spectra in the cold and warm neutral medium constraining the temperature and density of atomic gas as it transitions into molecular gas. Combined with radio continuum and molecular line data from the ngVLA plus multi-wavelength data from other planned facilities, ngVLA will have a key role in understanding star-formation in the local universe while complementing future studies with the Square Kilometer Array.