Red-Sequence Galaxies at High Redshift by the COMBO-17+4 Survey

TL;DR

This study examines the evolution of red-sequence galaxies since redshift 2, revealing their colour, mass density growth, and the early presence of massive galaxies, using combined optical and near-infrared data.

Contribution

It provides the first detailed analysis of the colour bimodality and mass density evolution of red-sequence galaxies up to z~1.65 with precise photometric redshifts.

Findings

Red sequence colour evolves linearly with lookback time.

Massive red galaxies increase in density by a factor of 4 from z~2 to 1.

Massive galaxies as early as z~2 are already in place.

Abstract

We investigate the evolution of the galaxy population since redshift 2 with a focus on the colour bimodality and mass density of the red sequence. We obtain precise and reliable photometric redshifts up to z=2 by supplementing the optical survey COMBO-17 with observations in four near-infrared bands on 0.2 square degrees of the COMBO-17 A901-field. Our results are based on an H-band-selected catalogue of 10692 galaxies complete to H=21.7. We measure the rest-frame colour (U_280-V) of each galaxy, which across the redshift range of our interest requires no extrapolation and is robust against moderate redshift errors by staying clear of the 4000A-break. We measure the colour-magnitude relation of the red sequence as a function of lookback time from the peak in a colour error-weighted histogram, and thus trace the galaxy bimodality out to z~1.65. The (U_280-V) of the red sequence is found to evolve almost linearly with lookback time. At high redshift, we find massive galaxies in both the red and the blue population. Red-sequence galaxies with log M_*/M_sun>11 increase in mass density by a factor of ~4 from z~2 to 1 and remain nearly constant at z<1. However, some galaxies as massive as log M_*/M_sun=11.5 are already in place at z~2.