The Stripe 82 Massive Galaxy Project. III. A Lack of Growth among Massive Galaxies

Abstract

The average stellar mass (M * ) of high-mass galaxies (log M * /M ⊙ > 11.5) 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 (s82-mgc) to build a mass-limited sample of 41,770 galaxies (log M * /M ⊙ > 11.2) with optical to near-IR photometry and a large fraction (>55%) of spectroscopic redshifts. Our sample spans 139 deg 2 , significantly larger than previous efforts. After accounting for a number of potential systematic errors, including the effects of M * scatter, we measure galaxy stellar mass functions over 0.3 < z < 0.65 and detect no growth in the typical M * of massive galaxies with an uncertainty of 9%. This confidence level is dominated by uncertainties in the star formation history assumed for M * 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 M ⊙ /yr) number density does not evolve. Interestingly, these galaxies become more prominent at higher M * , representing ∼10% of all galaxies at 10 12 M ⊙ and perhaps dominating at even larger masses.

On the (Lack of) Evolution of the Stellar Mass Function of Massive Galaxies from z = 1.5 to 0.4

“…At higher masses (log(M * /M ) > 11.5), the cosmic variance rises to 6%-12% ( Figure 23 in Appendix A). In the redshift range where we overlap with Bundy et al (2017), our cosmic variance is larger. This is expected as the area of S82MGC is 8 times larger than that of the SHELA.…”

“…For example, using the formalism set by Moster et al (2011), the relative cosmic variance, σ v , of galaxies more massive than 10 11 M at z = 0.35 is 36% (∼ 0.1 dex) for COSMOS (≈2 deg 2 ), but only ∼17% (∼ 0.07 dex) for SHELA. Bundy et al (2017) estimated the cosmic variance in the S82MGC (140 deg 2 ) using bootstrap resampling. In the 0.3 < z < 0.65 bin, their estimated 1σ error due to the cosmic variance is ∼ 0.01 dex (corresponding to σ v of ∼ 2%) at log(M * /M ) ∼ 11.0, and 0.02-0.05 dex (σ v ∼ 5% − 10%) at log(M * /M ) ∼ 11.6.…”

“…We adopt the method of Bundy et al (2017) to estimate the cosmic variance in our SHELA samples. We divide the SHELA survey into 150 roughly equal area regions and recompute stellar mass functions after resampling with replacement (see Appendix A).…”

“…To test for other sources of systematic uncertainty, we compare our SMF from SHELA to that in S82-MGC (Bundy et al 2017) for all galaxies between 0.3 < z < 0.65, where our samples overlap (see Section 7 and Figure 19). The two estimates, which both use the forward modeling method, are in good agreement.…”

“…This could significantly contribute to the total error budget, and consequently affect the robustness of the detected evolution of galaxy stellar mass function (Marchesini et al 2009). Bundy et al (2017) recently studied these issues and their effect on the evolution of the SMF by exploiting the Stripe 82 Massive Galaxy Catalog (S82-MGC) and constructing a mass-limited sample at 0.3 < z < 0.65 that is complete to M * > 10 11.3 M , over a large area of 140 deg 2 . After accounting for both random and systematic uncertainties, they reported no evolution in the characteristic stellar mass of the stellar mass function over the redshift range probed, contrasting with the findings of both Matsuoka & Kawara (2010) and Moutard et al (2016).…”