The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey. This catalog represents the largest homogeneous catalog of GC number and mass fractions across a wide range of galaxy luminosity (−22 < M B < −15). We find that 1) GC mass fractions can be high in both giants and dwarfs, but are universally low in galaxies with intermediate luminosities (−20 < M B < −17).2) The fraction of red GCs increases with galaxy luminosity, but stays constant or decreases for galaxies brighter than M z = −22. As a result, although specific frequencies for blue and red GCs are both higher in massive galaxies, the behavior of specific frequency across galaxy mass is dominated by the blue GCs.3) The GC fractions of low-mass galaxies exhibit a dependence on environment, where dwarf galaxies closer to the cluster center have higher GC fractions. Nearly all dwarfs with high GC fractions are within 1 Mpc of the cD galaxy M87, presenting the first strong evidence that GC formation in dwarf galaxies is biased toward dense environments. 4) GC formation in central dwarfs is biased because their stars form earliest and most intensely. Comparisons to early-type dwarf galaxies in the Millennium Simulation show that central dwarfs are likely to have older stellar populations and form more of their stars at higher star formation rates (SFRs) and star formation rate surface densities. In addition, the SFR surface density in simulated dwarfs peaks before the total SFR, naturally producing GC populations that are older and more metal-poor than the field stars. 5) Dwarfs within ∼ 40 kpc of the giant ellipticals M87 and M49 are red for their luminosities and have few or no GCs, suggesting that they have been tidally stripped and have contributed their GCs to the halos of their giant neighbors. The central dwarfs with high GC mass fractions are thus likely to be the survivors most similar to the protogalaxies that assembled the rich M87 globular cluster system.

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Using a large optically-selected sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey (PS1/MDS), we present a detailed analysis of the specific star formation rate (SSFR) -stellar mass (M * ) relation, as well as the quiescent fraction versus M * relation in different environments. While both the SSFR and the quiescent fraction depend strongly on stellar mass, the environment also plays an important role. Using this large galaxy sample, we confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments (M > 10 14 M ⊙ ), we find a global reduction in the SSFR of the star forming sequence of 17% at 4σ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass, although deeper and larger data from the full PS1/MDS will be required to draw firm conclusions. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass -the mass quenching plays a dominant role in producing quiescent galaxies for more massive galaxies, while less massive galaxies are quenched mostly through the environmental effect, with the transition mass around 1 − 2 × 10 10 M ⊙ in the group/cluster environment.