GMASS Ultradeep Spectroscopy of Galaxies at z~2. III: The emergence of the color bimodality at z~2

TL;DR

This study investigates the evolution of galaxy color distribution from redshift 1.4 to 3, revealing the emergence and decline of the bimodal color distribution and the properties of red galaxies at z~2.

Contribution

It provides new insights into the development of galaxy color bimodality and the morphological and star formation properties of red galaxies at high redshift.

Findings

Color bimodality persists up to z=2

Red early-type galaxy fraction decreases with redshift

Presence of passively evolving red galaxies at z>2

Abstract

The aim of this work is to study the evolution of the rest frame color distribution of galaxies with the redshift, in particular in the critical interval 1.4<z<3. We combine ultradeep spectroscopy from the GMASS project (Galaxy Mass Assembly ultradeep Spectroscopic Survey) with GOODS multi-band photometry (from optical to mid-infrared) to study a sample of 1021 galaxies up to m(4.5$\mu$m)=23. We find that the distribution of galaxies in the (U-B) color vs stellar mass plane is bimodal up to at least redshift z=2. We define a mass complete sample of galaxies residing on the red-sequence, selecting objects with log(M/M_{\odot})>10.1, and we study their morphological and spectro-photometric properties. We show that the contribution to this sample of early-type galaxies, defined as galaxies with a spheroidal morphology and no star formation, decreases from 60-70% at z<0.5 down to ~50% at redshift z=2. At z>2 we still find red galaxies in the mass complete sample, even if the bimodality is not seen any more. About 25% of these red galaxies at z>2 are passively evolving, with the bulk of their stars formed at redshift z>`3.