Environmental dependence of gas properties in a protocluster at z~2.5

TL;DR

This study investigates gas properties of galaxies in a z~2.5 protocluster, revealing enhanced gas masses and star formation in dense cores, consistent with efficient gas supply along filaments, without altering the star formation law.

Contribution

It provides new ALMA observations of dust continuum in protocluster galaxies, showing environmental effects on gas content and star formation at high redshift.

Findings

Galaxies in dense cores have higher gas to stellar mass ratios.

Gas properties follow the same scaling relations as field galaxies.

Enhanced star formation is driven by increased gas supply, not altered star formation laws.

Abstract

In a protocluster USS1558-003 at z=2.53, galaxies in the dense cores show systematically elevated star-forming activities than those in less dense regions. To understand its origin, we look into the gas properties of the galaxies in the dense cores by conducting deep 1.1mm observations with Atacama Large Millimeter/submillimeter Array (ALMA). We detect interstellar dust continuum emissions from 12 member galaxies and estimate their molecular gas masses. Comparing these gas masses with our previous measurements from CO(3-2) line, we infer that the latter might be overestimated. We find that the gas to stellar mass ratios of the galaxies in the dense cores tend to be higher (at M* ~ 10^{10} M_sun) where we see the enhanced star-forming activities), suggesting that such large gas masses can sustain their high star-forming activities. However, if we compare the gas properties of these protocluster galaxies with the gas scaling relations constructed for field galaxies at similar cosmic epoch, we find no significant environmental difference at the same stellar mass and star formation rate. Although both gas mass ratios and star-forming activities are enhanced in the majority of member galaxies, they appear to follow the same scaling relation as field galaxies. Our results are consistent with the scenario that the cold gas is efficiently supplied to protocluster cores and to galaxies therein along surrounding filamentary structures, which leads to the high gas mass fractions and thus the elevated star-formation activities, but without changing the star formation law.