VLA Large Program – Vz-GAL: Total Cold Gas Masses for 125 Dusty Massive Starbursts at z = 1–6

Vz-GAL (VLA/23B-169; PI: Riechers) is a new Karl G. Jansky Very Large Array (VLA) Large Program with the goal to observe the lowest rotational (J) levels of the CO molecule, i.e., the CO(J=1-0) and CO(J=2-1) emission lines from cold, star-forming gas in a sample of 125 starburst galaxies at redshifts between 1 and 6. These galaxies were selected from ~1000 suqre degrees of 250, 350, and 500 micron imaging surveys carried out with the Herschel Space Observatory. The entire sample has secure spectroscopic redshifts from the Northern Extended Millimeter Array (NOEMA) z-GAL Large Program based primarily on higher-level rotational transitions from the CO molecule and the forbidden [CI] fine structure lines from the carbon atom. While NOEMA is an excellent "redshift machine", the VLA is the currently best facility to detect the low-J CO lines, which are the best known indicator of total cold gas masses, i.e., the reservoirs for star formation powering the starbursts. Vz-GAL will result in the far largest reference sample for studies of the gas content, gas excitation, and gas-to-dust ratios in intensely star-forming galaxies in the early universe. The well-defined sample selection, combined with the substantially improved statistical significance of this study, will provide a legacy data set for the study of the gaseous evolution of galaxies which will remain unrivaled until the advent of the ngVLA.