Star-forming fractions and galaxy evolution with redshift in rich X-ray-selected galaxy clusters^⋆

¹ Departamento de AstronomíaUniversidad de Concepción, Casilla 160-C, Concepcion, Chile
e-mail: jnantais@astro-udec.cl
² Department of Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125, USA
³ Australian Astronomical Observatory, PO Box 296, Epping NSW 1710, Australia
⁴ Laboratoire AIM-Paris-Saclay, CEA/DSM-CNRS-Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
⁵ ESO, Karl-Schwarzchild Strasse 2, 85748 Garching, Germany
⁶ Department of Physics, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA

Received: 10 May 2013
Accepted: 12 June 2013

Abstract

We have compared stacked spectra of galaxies, grouped by environment and stellar mass, among 58 members of the redshift z = 1.24 galaxy cluster RDCS J1252.9-2927 (J1252.9) and 134 galaxies in the z = 0.84 cluster RX J0152.7-1357 (J0152.7). These two clusters are excellent laboratories to study how galaxies evolve from star-forming to passive at z ~ 1. We measured spectral indices and star-forming fractions for our density- and mass-based stacked spectra. The star-forming fraction among low-mass galaxies (<7 × 10¹⁰M_⊙) is higher in J1252.9 than in J0152.7, at about 4σ significance. Thus star formation is being quenched between z = 1.24 and z = 0.84 for a substantial fraction of low-mass galaxies. Star-forming fractions were also found to be higher in J1252.9 in all environments, including the core. Passive galaxies in J1252.9 have systematically lower D_n4000 values than in J0152.7 in all density and mass groups, consistent with passive evolution at modestly super-solar metallicities.