K+a galaxies in the zCOSMOS Survey: Physical properties of systems in their post-starburst phase

TL;DR

This study investigates the physical properties and environmental contexts of k+a post-starburst galaxies in the zCOSMOS survey, revealing their heterogeneity, mass distribution, and potential role in galaxy evolution.

Contribution

It provides a detailed multiwavelength analysis of k+a galaxies at intermediate redshifts, highlighting their morphological diversity and environmental similarities to quiescent galaxies.

Findings

K+a galaxies are among the brightest and most massive in their luminosity distribution.

They are morphologically diverse, with similar bulge and disk fractions across the sample.

No significant evolution in their number or spectral properties over the studied redshift range.

Abstract

The identities of the main processes triggering and quenching star-formation in galaxies remain unclear. A key stage in evolution, however, appears to be represented by post-starburst galaxies. To investigate their impact on galaxy evolution, we initiated a multiwavelength study of galaxies with k+a spectral features in the COSMOS field. We examine a mass-selected sample of k+a galaxies at z=0.48-1.2 using the spectroscopic zCOSMOS sample. K+a galaxies occupy the brightest tail of the luminosity distribution. They are as massive as quiescent galaxies and populate the green valley in the colour versus luminosity (or stellar mass) distribution. A small percentage (<8%) of these galaxies have radio and/or X-ray counterparts (implying an upper limit to the SFR of ~8Msun/yr). Over the entire redshift range explored, the class of k+a galaxies is morphologically a heterogeneous population with a similar incidence of bulge-dominated and disky galaxies. This distribution does not vary with the strength of the Hdelta absorption line but instead with stellar mass in a way reminiscent of the well-known mass-morphology relation. Although k+a galaxies are also found in underdense regions, they appear to reside typically in a similarly rich environment as quiescent galaxies on a physical scale of ~2-8Mpc, and in groups they show a morphological early-to-late type ratio similar to the quiescent galaxy class. With the current data set, we do not find evidence of statistical significant evolution in either the number/mass density of k+a galaxies at intermediate redshift with respect to the local values, or the spectral properties. Those galaxies, which are affected by a sudden quenching of their star-formation activity, may increase the stellar mass of the red-sequence by up to a non-negligible level of ~10%.