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

TL;DR

This study compares galaxy spectra in two rich X-ray-selected clusters at different redshifts to understand galaxy evolution and star formation quenching over cosmic time.

Contribution

It provides new insights into how star-forming fractions decrease with time, especially for low-mass galaxies, using spectral analysis of two galaxy clusters at z=1.24 and z=0.84.

Findings

Star-forming fraction is higher at z=1.24 for low-mass galaxies.

Star formation quenching occurs between z=1.24 and z=0.84.

Passive galaxies show lower D_n4000 values at higher redshift.

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 x 10^10 M_sun) is higher in J1252.9 than in J0152.7, at about 4 sigma 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.