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THE GLOBULAR CLUSTER SYSTEM OF NGC 4636 AND FORMATION OF GLOBULAR CLUSTERS IN GIANT ELLIPTICAL GALAXIES

2012; IOP Publishing; Volume: 759; Issue: 2 Linguagem: Inglês

10.1088/0004-637x/759/2/116

1538-4357

Hong Soo Park, Myung Gyoon Lee, Ho Seong Hwang, Sang Chul Kim, N. Arimoto, Yoshihiko Yamada, Naoyuki Tamura, Masato Onodera,

Astronomy and Astrophysical Research

We present a spectroscopic analysis of the metallicities, ages, and alpha-elements of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo Cluster. Line indices of the GCs are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph on the Subaru 8.2 m Telescope. We derive [Fe/H] values of 59 GCs based on the Brodie & Huchra method, and [Z/H], age, and [α/Fe] values of 33 GCs from the comparison of the Lick line indices with single stellar population models. The metallicity distribution of NGC 4636 GCs shows a hint of a bimodality with two peaks at [Fe/H] = -1.23(σ = 0.32) and −0.35(σ = 0.19). The age spread is large from 2 Gyr to 15 Gyr and the fraction of young GCs with age 99.9%. All these gEs harbor some young GCs with ages less than 5 Gyr. 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 value of [α/Fe] of the gE GCs is smaller than that of the Milky Way GCs. We discuss these results in the context of GC formation in gEs.