Extragalactic Globular Clusters: Old Spectroscopic Ages and New Views on   Their Formation
  We present the results of a meta-analysis of Keck spectra of extragalactic globular clusters (GCs) in a sample of eight galaxies, ranging from dwarfs to massive ellipticals. We infer ages for the metal-poor and metal-rich GCs in these galaxies through comparisons to Galactic GCs. Both subpopulations appear to be no younger than their Galactic counterparts, with ages ~> 10 Gyr. This is the largest sample of galaxies for which ages have been constrained spectroscopically. Our results support the formation of most GCs in massive galaxies at high redshift. We propose a scenario for the formation of GC subpopulations that synthesizes aspects of both accretion and in situ approaches in the context of galaxy formation through hierarchical merging. 
Jay Strader (1), Jean P. Brodie (1), A. J. Cenarro (1,2), Michael A.   Beasley (1), Duncan A. Forbes (3), ((1) UCO/Lick Obse...