ALMA's View of Molecular Gas in the Core of a High-Redshift Galaxy Protocluster

Massive Lyman-alpha nebulae have long been used to trace warm reservoirs of gas at high redshifts. Previous observations have detected one of the largest of these nebulae known to date, MAMMOTH-I, coinciding with the core of a galaxy protocluster at a redshift of 2.3116. Such proto-cluster cores are believed to be the progenitors of giant elliptical galaxies found in galaxy clusters in the local universe. In order to learn how these cores evolve in terms of stellar formation, we imaged cold molecular gas -the raw ingredient for star formation- across the Lyman-alpha nebula of MAMMOTH-I with 3 molecular line emissions: CO(4-3) and [CI] from the Atacama Large Millimeter/submillimeter Array (ALMA) and CO(1-0) from the Karl G. Jansky Very Large Array (VLA). We find evidence of molecular gas extending into the circumgalactic medium in both CO(1-0) and [CI] while CO(4-3) emission is localized to proto-cluster galaxies and shows no signs of this extended structure, reinforcing the idea that the high-J CO line transitions may not be as strong of a tracer for extended molecular gas. The ratios of the line luminosities show that the molecular gas across the MAMMOTH-I Nebula has properties similar to that of interstellar mediums in local star forming galaxies. These results help to understand the details of the evolution of galaxy proto-clusters in early Universe.