Evidence for an Intermediate‐Age, Metal‐rich Population of Globular Clusters in NGC 4365

We present spectroscopy for globular clusters (GCs) in the elliptical galaxy NGC 4365, obtained with the Low-Resolution Imaging Spectrograph on the Keck I telescope. Previous studies have shown that the optical color distribution of GCs in NGC 4365 lacks the bimodal structure that is common in globular cluster systems, showing only a single broad peak. Measurements of Balmer line indices (Hβ, Hγ, and Hδ) on the GC spectra support recent suggestions by Puzia et al. on the basis of optical and near-infrared photometry that some of the clusters in NGC 4365 are intermediate-age (2-5 Gyr) and metal-rich (-0.4 ≲ [Z/H] ≲ 0) rather than old (~10-15 Gyr) and metal-poor. We also find some genuinely metal-poor, old clusters, suggesting that the ages and metallicities of the two populations conspire to produce the single broad distribution observed in optical colors.