Revealing environmental dependence of molecular gas content in a distant X-ray cluster at z=2.51

TL;DR

This study investigates how the environment influences molecular gas content and star formation efficiency in galaxies within a distant galaxy cluster at redshift 2.51, revealing environmental dependence and implications for galaxy evolution.

Contribution

It provides the first detailed CO(1-0) measurements of a large galaxy sample in a z>2 cluster, demonstrating environmental effects on gas content and star formation.

Findings

Gas content varies with cluster position, decreasing towards the core.

Galaxies in the cluster center have higher star formation efficiency.

Gas depletion time is about 400 Myrs, indicating rapid gas consumption.

Abstract

We present a census of the molecular gas properties of galaxies in the most distant known X-ray cluster, CLJ1001, at z=2.51, using deep observations of CO(1-0) with JVLA. In total 14 cluster members with $M_{*} > 10^{10.5} M_{\odot}$ are detected, including all the massive star-forming members within the virial radius, providing the largest galaxy sample in a single cluster at $z > 2$ with CO(1-0) measurements. We find a large variety in the gas content of these cluster galaxies, which is correlated with their relative positions (or accretion states), with those closer to the cluster core being increasingly gas-poor. Moreover, despite their low gas content, the galaxies in the cluster center exhibit an elevated star formation efficiency (SFE=SFR/$M_{\rm gas}$) compared to field galaxies, suggesting that the suppression on the SFR is likely delayed compared to that on the gas content. Their gas depletion time is around $t_{\rm dep} \sim 400$ Myrs, comparable to the cluster dynamical time. This implies that they will likely consume all their gas within a single orbit around the cluster center, and form a passive cluster core by $z\sim2$. This result is one of the first direct pieces of evidence for the influence of environment on the gas reservoirs and SFE of $z > 2$ cluster galaxies, thereby providing new insights into the rapid formation and quenching of the most massive galaxies in the early universe.