Molecular gas reservoirs in cluster galaxies at z=1.46

TL;DR

This study investigates molecular gas in 18 galaxies within a z=1.46 galaxy cluster using ALMA, revealing larger gas fractions and longer depletion times than in field galaxies, with environmental effects influencing star formation and gas content.

Contribution

First detailed ALMA observations of molecular gas in cluster galaxies at z=1.46, showing environmental impacts on gas properties and star formation activity.

Findings

Cluster galaxies have higher molecular gas fractions than expected.

Galaxies near the cluster center show larger deviations from scaling relations.

Massive quiescent galaxies in the core lack detectable CO emission.

Abstract

We present molecular gas reservoirs of eighteen galaxies associated with the XMMXCS J2215.9-1738 cluster at z=1.46. From Band 7 and Band 3 data of the Atacama Large Millimeter/submillimeter Array (ALMA), we detect dust continuum emission at 870 um and CO J=2-1 emission line from 8 and 17 member galaxies respectively within a cluster-centric radius of $R_{200}$. The molecular gas masses derived from the CO and/or dust continuum luminosities show that the fraction of molecular gas mass and the depletion time scale for the cluster galaxies are larger than expected from the scaling relations of molecular gas on stellar mass and offset from the main sequence of star-forming galaxies in general fields. The galaxies closer to the cluster center in terms of both projected position and accretion phase seem to show a larger deviation from the scaling relations. We speculate that the environment of galaxy cluster helps feed the gas through inflow to the member galaxies and also reduce the efficiency of star formation. The stacked Band 3 spectrum of 12 quiescent galaxies with stellar mass $\sim10^{11}$ M$_\odot$ within 0.5$R_{200}$ shows no detection of CO emission line, giving the upper limit of molecular gas mass and molecular gas fraction to be $<10^{10}$ M$_\odot$ and $<10$%, respectively. Therefore, the massive galaxies in the cluster core quench the star formation activity while consuming most of the gas reservoirs.