The Evolving Luminosity Function of Red Galaxies

Abstract

We trace the assembly history of red galaxies since z=1, by measuring their evolving space density with the B-band luminosity function. Our sample of 39599 red galaxies, selected from 6.96 square degrees of imaging from the NOAO Deep Wide-Field and Spitzer IRAC Shallow surveys, is an order of magnitude larger, in size and volume, than comparable samples in the literature. We measure a higher space density of z=0.9 red galaxies than some of the recent literature, in part because we account for the faint yet significant galaxy flux which falls outside of our photometric aperture. The B-band luminosity density of red galaxies, which effectively measures the evolution of ~L* galaxies, increases by only 36 percent from z=0 to z=1. If red galaxy stellar populations have faded by 1.24 B-band magnitudes since z=1, the stellar mass contained within the red galaxy population has roughly doubled over the past 8 Gyr. This is consistent with star-forming galaxies being transformed into ~L* red galaxies after a decline in their star formation rates. In contrast, the evolution of 4L* red galaxies differs only slightly from a model with negligible star formation and no galaxy mergers since z=1. If this model approximates the luminosity evolution of red galaxy stellar populations, then 80 percent of the stellar mass contained within today's 4L* red galaxies was already in place at z=0.7. While red galaxy mergers have been observed, such mergers do not produce rapid growth of 4L* red galaxy stellar masses between z=1 and the present day.