The Detection of a Red Sequence of Massive Field Galaxies at z~2.3 and its Evolution to z~0

TL;DR

This study identifies a significant red sequence of massive, mostly post-starburst galaxies at z~2.3 and analyzes its evolution to the present, showing substantial growth in number and stellar mass density over time.

Contribution

It provides the first evidence of a red sequence at z~2.3 and models its evolution, highlighting the roles of galaxy transformations and mergers.

Findings

A significant red sequence exists at z~2.3, hosting ~60% of stellar mass.

The red sequence's color reddens by ~0.25 mag from z~2.3 to z~0.

Number and mass density of massive red galaxies increase by factors of ~8 and ~6, respectively.

Abstract

The existence of massive galaxies with strongly suppressed star formation at z~2.3, identified in a previous paper, suggests that a red sequence may already be in place beyond z=2. In order to test this hypothesis, we study the rest-frame U-B color distribution of massive galaxies at 2<z<3. The sample is drawn from our near-infrared spectroscopic survey for massive galaxies. The color distribution shows a statistically significant (>3 sigma) red sequence, which hosts ~60% of the stellar mass at the high-mass end. The red-sequence galaxies have little or no ongoing star formation, as inferred from both emission-line diagnostics and stellar continuum shapes. Their strong Balmer breaks and their location in the rest-frame U-B, B-V plane indicate that they are in a post-starburst phase, with typical ages of ~0.5-1.0 Gyr. In order to study the evolution of the red sequence, we compare our sample with spectroscopic massive galaxy samples at 0.02<z<0.045 and 0.6<z<1.0. The rest-frame U-B color reddens by ~0.25 mag from z~2.3 to the present at a given mass. Over the same redshift interval, the number and stellar mass density on the high-mass end (>10^11 Msol) of the red sequence grow by factors of ~8 and ~6, respectively. We explore simple models to explain the observed evolution. Passive evolution models predict too strong d(U-B), and produce z~0 galaxies that are too red. More complicated models that include aging, galaxy transformations, and red mergers can explain both the number density and color evolution of the massive end of the red sequence between z~2.3 and the present.