Witnessing the active assembly phase of massive galaxies since z = 1

TL;DR

This study analyzes the growth and evolution of massive galaxies since redshift 1, revealing rapid increases in the most massive galaxies and a decline in blue star-forming galaxies, supporting hierarchical galaxy formation models.

Contribution

It provides the largest robust dataset of massive galaxies up to z=1, confirming hierarchical growth and the active assembly of massive galaxies over cosmic time.

Findings

Most massive galaxies increased rapidly in number since z=1

Less massive galaxies showed mild evolution in number density

Red, massive galaxies dominate at low redshift

Abstract

We present an analysis of ~60 000 massive (stellar mass M_star > 10^{11} M_sun) galaxies out to z = 1 drawn from 55.2 deg2 of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) and the Sloan Digital Sky Survey (SDSS) II Supernova Survey. This is by far the largest survey of massive galaxies with robust mass estimates, based on infrared (K-band) photometry, reaching to the Universe at about half its present age. We find that the most massive (M_star > 10^{11.5} M_sun) galaxies have experienced rapid growth in number since z = 1, while the number densities of the less massive systems show rather mild evolution. Such a hierarchical trend of evolution is consistent with the predictions of the current semi-analytic galaxy formation model based on Lambda CDM theory. While the majority of massive galaxies are red-sequence populations, we find that a considerable fraction of galaxies are blue star-forming galaxies. The blue fraction is smaller in more massive systems and decreases toward the local Universe, leaving the red, most massive galaxies at low redshifts, which would support the idea of active 'bottom-up' formation of these populations during 0 < z < 1.