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 1Â 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 \sim 40 Â 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 .