PRIMUS: Constraints on Star Formation Quenching and Galaxy Merging, and the Evolution of the Stellar Mass Function From z=0-1

We measure the evolution of the stellar mass function (SMF) from z=0-1 using multi-wavelength imaging and spectroscopic redshifts from the PRism MUlti-object Survey (PRIMUS) and the Sloan Digital Sky Survey (SDSS). From PRIMUS we construct an i<23 flux-limited sample of ~40,000 galaxies at z=0.2-1.0 over five fields totaling ~5.5 deg^2, and from the SDSS we select ~170,000 galaxies at z=0.01-0.2 that we analyze consistently with respect to PRIMUS to minimize systematic errors in our evolutionary measurements. We find that the SMF of all galaxies evolves relatively little since z=1, although we do find evidence for mass assembly downsizing; we measure a ~30% increase in the number density of ~10^10 Msun galaxies since z~0.6, and a <10% change in the number density of all >10^11 Msun galaxies since z~1. Dividing the sample into star-forming and quiescent using an evolving cut in specific star-formation rate, we find that the number density of ~10^10 Msun star-forming galaxies stays relatively constant since z~0.6, whereas the space-density of >10^11 Msun star-forming galaxies decreases by ~50% between z~1 and z~0. Meanwhile, the number density of ~10^10 Msun quiescent galaxies increases steeply towards low redshift, by a factor of ~2-3 since z~0.6, while the number of massive quiescent galaxies remains approximately constant since z~1. These results suggest that the rate at which star-forming galaxies are quenched increases with decreasing stellar mass, but that the bulk of the stellar mass buildup within the quiescent population occurs around ~10^10.8 Msun. In addition, we conclude that mergers do not appear to be a dominant channel for the stellar mass buildup of galaxies at z<1, even among massive (>10^11 Msun) quiescent galaxies.