The ACS Fornax Cluster Survey. III. Globular Cluster Specific Frequencies of Early-type Galaxies

The globular cluster (GC) specific frequency (S _N), defined as the number of GCs per unit galactic luminosity, represents the efficiency of GC formation (and survival) compared to field stars. Despite the naive expectation that star cluster formation should scale directly with star formation, this efficiency varies widely across galaxies. To explore this variation, we measure the z-band GC specific frequency () for 43 early-type galaxies (ETGs) from the Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) Fornax Cluster Survey. Combined with the homogeneous measurements of in 100 ETGs from the HST/ACS Virgo Cluster Survey from Peng et al., we investigate the dependence of on mass and environment over a range of galaxy properties. We find that behaves similarly in the two galaxy clusters, despite the clusters' order-of-magnitude difference in mass density. The is low in intermediate-mass ETGs (-20 < M _z < -23) and increases with galaxy luminosity. It is elevated at low masses, on average, but with a large scatter driven by galaxies in dense environments. The densest environments with the strongest tidal forces appear to strip the GC systems of low-mass galaxies. However, in low-mass galaxies that are not in strong tidal fields, denser environments correlate with enhanced GC formation efficiencies. Normalizing by inferred halo masses, the GC mass fraction, η = (3.36 ±; 0.2) × 10^-5, is constant for ETGs with stellar masses M_∗≲ 3 × 10¹⁰ M_O, in agreement with previous studies. The lack of correlation between the fraction of GCs and the nuclear light implies only a weak link between the infall of GCs and the formation of nuclei.