Evolution of Cluster Red-Sequence Galaxies from redshift 0.8 to 0.4: ages, metallicities and morphologies

TL;DR

This study analyzes the evolution of stellar populations and morphologies of red-sequence galaxies in clusters from redshift 0.75 to 0.45, revealing mass-dependent evolution and a gradual morphological transformation.

Contribution

It provides the largest spectroscopic analysis of red-sequence galaxies at these redshifts, showing how their properties evolve with mass and time, and how star formation quenching relates to morphological changes.

Findings

Massive galaxies follow passive evolution with high-redshift formation.

Less massive galaxies have extended star formation histories.

The fraction of early-type morphologies decreases by 20% from z=0.75 to 0.45.

Abstract

We present a comprehensive analysis of the stellar population properties (age, metallicity and the alpha-element enhancement [E/Fe]) and morphologies of red-sequence galaxies in 24 clusters and groups from z~0.75 to z~0.45. The dataset, consisting of 215 spectra drawn from the ESO Distant Cluster Survey, constitutes the largest spectroscopic sample at these redshifts for which such an analysis has been conducted. Analysis reveals that the evolution of the stellar population properties of red-sequence galaxies depend on their mass: while the properties of most massive are well described by passive evolution and high-redshift formation, the less massive galaxies require a more extended star formation history. We show that these scenarios reproduce the index-sigma relations as well as the galaxy colours. The two main results of this work are (1) the evolution of the line-strength indices for the red-sequence galaxies can be reproduced if 40% of the galaxies with sigma < 175 km/s entered the red-sequence between z=0.75 to z=0.45, in agreement with the fraction derived in studies of the luminosity functions, and (2) the percentage the red-sequence galaxies exhibiting early-type morphologies (E and S0) decreases by 20% from z=0.75 to z=0.45. This can be understood if the red-sequence gets populated at later times with disc galaxies whose star formation has been quenched. We conclude that the processes quenching star formation do not necessarily produce a simultaneous morphological transformation of the galaxies entering the red-sequence.