Imaging Molecular Gas at High Redshift

TL;DR

This paper simulates the next-generation VLA's ability to image molecular gas in high-redshift galaxies at 1 kpc resolution, demonstrating its potential to recover galaxy dynamics and structure more efficiently than current facilities.

Contribution

It introduces a simulation framework for the ngVLA's capabilities in high-resolution imaging of molecular gas in distant galaxies, highlighting its advantages over existing telescopes.

Findings

ngVLA can image molecular gas at 1 kpc resolution in high-redshift galaxies.

It can recover galaxy rotation curves and orientation parameters.

Current facilities like ALMA and VLA lack the sensitivity for such high-resolution imaging.

Abstract

We perform simulations of the capabilities of the next generation Very Large Array in the context of imaging low order CO emission from typical high redshift star forming galaxies at ~ 1 kpc resolution. We adopt as a spatial and dynamical template the CO 1-0 emission from M 51, scaled accordingly for redshift, transition, and total gas mass. The molecular gas masses investigated are factors of 1.4, 3.5, and 12.5 larger that of M 51, at z = 0.5, 2, and 4.2, respectively. The z = 2 galaxy gas mass is comparable to the lowest mass galaxies currently being discovered in the deepest ALMA and NOEMA cosmological CO line surveys, corresponding to galaxies with star formation rates ~ 10 to 100 $M_\odot$ yr$^{-1}$. The ngVLA will perform quality imaging at 1kpc resolution of the gas distribution and dynamics over this disk. We recover the overall rotation curve, galaxy orientation properties, and molecular ISM internal velocity dispersion. The model at z = 4.2 corresponds to a massive star forming main sequence disk (SFR ~ 130 $M_\odot$ yr$^{-1}$). The ngVLA can obtain 1kpc resolution images of such a system in a reasonable integration time, and recover the basic galaxy orientation parameters, and, asymptotically, the maximum rotation velocity. We compare the ngVLA results with capabilities of ALMA and the Jansky VLA. ALMA and the VLA can detect the integrated low order CO emission from these galaxies, but lack the sensitivity to perform the high resolution imaging to recover the dynamics at 1kpc scales. To do so would require of order 1000 hrs per galaxy with these current facilities. We investigate a 'minimal' ngVLA configuration, removing the longest baselines and much of the very compact core, and find good imaging can still be performed at 1 kpc resolution.