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 arcmin 2 in spatial direction. The lines are all identified as CO J  = 2–1 emission lines from cluster members at by their redshifts and the colors of their optical and near-infrared (NIR) counterparts. The line luminosities reach down to K km s −1 pc 2 . 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.