Science with an ngVLA: Imaging Cold Gas to 1 kpc Scales in High-Redshift
  Galaxies with the ngVLA
  The next generation Very Large Array (ngVLA) will revolutionize our
understanding of the distant Universe via the detection of cold molecular gas
in the first galaxies. Its impact on studies of galaxy characterization via
detailed gas dynamics will provide crucial insight on dominant physical drivers
for star-formation in high redshift galaxies, including the exchange of gas
from scales of the circumgalactic medium down to resolved clouds on mass scales
of $\sim10^{5}\,M_\odot$. In this study, we employ a series of high-resolution,
cosmological, hydrodynamic zoom simulations from the MUFASA simulation suite
and a CASA simulator to generate mock ngVLA observations of a $z\sim4.5$ gas
rich star-forming galaxy. Using the DESPOTIC radiative transfer code that
encompasses simultaneous thermal, chemical, and statistical equilibrium in
calculating the molecular and atomic level transitions of CO from ALMA for
comparison. We find that observations of CO(1-0) are especially important for
tracing the systemic redshift of the galaxy and the total mass of the
well-shielded molecular gas reservoir, while even CO(2-1) can predominantly
trace denser gas regions distinct from CO(1-0). The factor of 100 times
improvement in mapping speed for the ngVLA beyond the Jansky VLA and the
proposed ALMA Band 1 will make these detailed, high-resolution imaging and
kinematic studies of CO(1-0) routine at $z\sim2-5$.
