# Environmental impacts on molecular gas in protocluster galaxies at z~2

## TL;DR

This study uses ALMA CO(3-2) observations to explore how dense protocluster environments at z~2 influence molecular gas properties in galaxies, revealing mass-dependent environmental effects on gas accretion and depletion.

## Contribution

It provides the first detailed analysis of molecular gas in protocluster galaxies at z~2, highlighting environment-driven differences based on galaxy mass.

## Key findings

- Less massive protocluster galaxies have higher gas fractions and longer depletion times.
- Massive galaxies show similar or reduced molecular gas compared to field relations.
- Environmental effects on gas are more pronounced in less massive galaxies.

## Abstract

We present the results from ALMA CO(3-2) observations of 66 Halpha-selected galaxies in three protoclusters around radio galaxies, PKS1138-262 (z=2.16) and USS1558-003 (z=2.53), and 4C23.56 (z=2.49). The pointing areas have an overdensity of ~100 compared to a mean surface number density of galaxies in field environments. We detect CO emission line in 16 star-forming galaxies, including previously published six galaxies, to measure the molecular gas mass. In the stellar mass range of 10.5<log(Mstar/Msolar)<11.0, the protocluster galaxies have larger gas mass fractions and longer gas depletion timescales compared to the scaling relations established by field galaxies. On the other hand, the amounts of molecular gas in more massive galaxies with log(Mstar/Msolar)>11.0 are comparable in mass to the scaling relation, or smaller. Our results suggest that the environmental effects on gas properties are mass-dependent: in high-density environments, gas accretion through cosmic filaments is accelerated in less massive galaxies while this is suppressed in the most massive system.