SEEDisCS

I. Molecular gas in galaxy clusters and their large-scale structure: The case of CL1411.1−1148 at z ∼ 0.5

¹ Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
e-mail: damien.sperone-longin@epfl.ch
² GEPI, Observatoire de Paris, PSL University, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
³ Observatoire de Paris, LERMA, CNRS, Sorbonne University, PSL Research University, 75014 Paris, France
⁴ Collège de France, 11 Place Marcelin Berthelot, 75231 Paris, France
⁵ IRAM, Domaine Universitaire, 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
⁶ Department of Physics and Astronomy, The University of Kansas, Lawrence, KS, USA
⁷ Steward Observatory and Department of Astronomy, University of Arizona, Tucson, AZ, USA
⁸ Department of Physics and Astronomy, Siena College, Loudonville, NY, USA
⁹ INAF – Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34143 Trieste, Italy
¹⁰ IPAC, Mail Code 100-22, Caltech, 1200 E. California Boulevard Pasadena, CA, USA

Received: 13 July 2020
Accepted: 19 January 2021

Abstract

We investigate how the galaxy reservoirs of molecular gas fuelling star formation are transformed while the host galaxies infall onto galaxy cluster cores. As part of the Spatially Extended ESO Distant Cluster Survey (SEEDisCS), we present CO(3-2) observations of 27 star-forming galaxies obtained with the Atacama Large Millimeter Array. These sources are located inside and around CL1411.1−1148 at z = 0.5195, within five times the cluster virial radius. These targets were selected to have stellar masses (M_star), colours, and magnitudes similar to those of a field comparison sample at similar redshift drawn from the Plateau de Bure high-z Blue Sequence Survey (PHIBSS2). We compare the cold gas fraction (μ_H2 = M_H2/M_star), specific star formation rates (SFR/M_star) and depletion timescales (t_depl = M_H2/SFR) of our main-sequence galaxies to the PHIBSS2 subsample. While the most of our galaxies (63%) are consistent with PHIBSS2, the remainder fall below the relation between μ_H2 and M_star of the PHIBSS2 galaxies at z ∼ 0.5. These low-μ_H2 galaxies are not compatible with the tail of a Gaussian distribution, hence they correspond to a new population of galaxies with normal SFRs but low gas content and low depletion times (≲1 Gyr), absent from previous surveys. We suggest that the star formation activity of these galaxies has not yet been diminished by their low fraction of cold molecular gas.