The Stripe 82 Massive Galaxy Project III: A Lack of Growth Among Massive
  Galaxies
  The average stellar mass (Mstar) of high-mass galaxies (Mstar > 3e11 Msun) is
expected to grow by ~30% since z~1, largely through ongoing mergers that are
also invoked to explain the observed increase in galaxy sizes. Direct evidence
for the corresponding growth in stellar mass has been elusive, however, in part
because the volumes sampled by previous redshift surveys have been too small to
yield reliable statistics. In this work, we make use of the Stripe 82 Massive
Galaxy Catalog to build a mass-limited sample of 41,770 galaxies (Mstar >
1.6e11) with optical to near-IR photometry and a large fraction (>55%) of
spectroscopic redshifts. Our sample spans 139 square degrees, significantly
larger than most previous efforts. After accounting for a number of potential
systematic errors, including the effects of Mstar scatter, we measure galaxy
stellar mass functions over 0.3 < z < 0.65 and detect no growth in the typical
Mstar of massive galaxies with an uncertainty of 9%. This confidence level is
dominated by uncertainties in the star formation history assumed for Mstar
estimates, although our inability to characterize low surface-brightness
outskirts may be the most important limitation of our study. Even among these
high-mass galaxies, we find evidence for differential evolution when splitting
the sample by recent star formation (SF) activity. While low-SF systems appear
to become completely passive, we find a mostly sub-dominant population of
galaxies with residual, but low rates of star formation (~1 Msun/yr) number
density does not evolve. Interestingly, these galaxies become more prominent at
higher Mstar, representing ~10% of all galaxies at Mstar ~ 1e12 Msun and
perhaps dominating at even larger masses.
