Chemical Properties of Globular Clusters in Nearby Giant Elliptical Galaxies

We present a study of the metallicities, ages, and alpha-elements of globular clusters (GCs) in nearby giant elliptical galaxies (gEs) (M87, M49, M60, NGC 5128, NGC 1399, NGC 1407, and NGC 4636) using data in the literature. We used only the data for the GCs derived from the comparison of absorption line indices with the single stellar population model. The metallicity distributions of GCs in these gEs are bimodal, showing the existence of metal-poor and metal-rich populations. All these gEs harbor young GCs with ages less than 5 Gyr as well as old GCs. The mean age of the metal-rich GCs ([Fe/H]>-0.9) is about 3 Gyr younger than that of the metal-poor GCs. The mean values for the alpha-elements of the GCs are smaller than or similar to that of the Milky Way GCs. All the GCs in these gEs show an age-metallicity relation; the larger the metallicities of the GCs are, the younger the GCs are. Old GCs with ages > 10 Gyr have two distinct sub-populations (metal poor and metal rich), while young GCs show a broad metallicity distribution with a single peak. We discuss these results in relation with the formation of GCs in gEs.