Evolutionary Phases of Gas-rich Galaxies in a Galaxy Cluster at z = 1.46

Abstract

We report a survey of molecular gas in galaxies in the XMMXCS J2215.9-1738 cluster at z = 1.46. We have detected emission lines from 17 galaxies within a radius of R ₂₀₀ from the cluster center, in Band 3 data of the Atacama Large Millimeter/submillimeter Array, with a coverage of 93-95 GHz in frequency and 2.33 arcmin² in spatial direction. The lines are all identified as CO J = 2-1 emission lines from cluster members at z∼ 1.46 by their redshifts and the colors of their optical and near-infrared (NIR) counterparts. The line luminosities reach down to {L}_{CO(2{--}1)}^\prime =4.5× {10}⁹ K km s^-1 pc². The spatial distribution of galaxies with a detection of CO(2-1) suggests that they disappear from the very center of the cluster. The phase-space diagram showing relative velocity versus cluster-centric distance indicates that the gas-rich galaxies have entered the cluster more recently than the gas-poor star-forming galaxies and passive galaxies located in the virialized region of this cluster. The results imply that the galaxies experienced ram-pressure stripping and/or strangulation during the course of infall toward the cluster center and then the molecular gas in the galaxies at the cluster center was depleted by star formation.