Molecular gas in a gravitationally lensed galaxy group at $z = 2.9$

TL;DR

This study uses ALMA observations of a gravitationally lensed galaxy group at z=2.9 to measure molecular gas content, revealing how gas depletion times vary with redshift and environment, especially in overdense regions.

Contribution

First measurement of molecular gas in a normal galaxy group at high redshift using gravitational lensing, providing insights into galaxy evolution in dense environments.

Findings

Depletion times decrease with increasing redshift.

Galaxies in overdense environments have steeper depletion time evolution.

Detected galaxies have molecular gas masses of (0.2-13.1) x 10^{10} M_sun.

Abstract

Most molecular gas studies of $z > 2.5$ galaxies are of intrinsically bright objects, despite the galaxy population being primarily "normal" galaxies with less extreme star formation rates. Observations of normal galaxies at high redshift provide a more representative view of galaxy evolution and star formation, but such observations are challenging to obtain. In this work, we present ALMA $\rm ^{12}CO(J = 3 \rightarrow 2)$ observations of a sub-millimeter selected galaxy group at $z = 2.9$, resulting in spectroscopic confirmation of seven images from four member galaxies. These galaxies are strongly lensed by the MS 0451.6-0305 foreground cluster at $z = 0.55$, allowing us to probe the molecular gas content on levels of $\rm 10^9-10^{10} \; M_\odot$. Four detected galaxies have molecular gas masses of $\rm (0.2-13.1) \times 10^{10} \; M_\odot$, and the non-detected galaxies have inferred molecular gas masses of $\rm < 8.0 \times 10^{10} \; M_\odot$. We compare these new data to a compilation of 546 galaxies up to $z = 5.3$, and find that depletion times decrease with increasing redshift. We then compare the depletion times of galaxies in overdense environments to the field scaling relation from the literature, and find that the depletion time evolution is steeper for galaxies in overdense environments than for those in the field. More molecular gas measurements of normal galaxies in overdense environments at higher redshifts ($z > 2.5$) are needed to verify the environmental dependence of star formation and gas depletion.