Stellar Populations of Globular Clusters in the Elliptical Galaxy NGC 1407

Abstract

We present high-quality Keck spectroscopic data for a sample of 20globular clusters (GCs) in the massive E0 galaxy NGC 1407. A subset of20 line-strength indices of the Lick/IDS system has been measured forboth the GC system and the central integrated starlight of the galaxy.Ages, metallicities, and [{α}/Fe] ratios have been derived usingseveral different approaches. The majority of GCs in NGC 1407 studiedare old, follow a tight metallicity sequence reaching values slightlyabove solar, and exhibit mean [{α}/Fe] ratios of ~0.3 dex. Inaddition, three GCs are formally derived to be young (~4 Gyr), but weargue that they are actually old GCs hosting blue horizontal branches.We report, for the first time, evidence for the existence of twochemically distinct subpopulations of metal-rich (MR) GCs. We find thatsome MR GCs exhibit significantly larger [Mg/Fe] and [C/Fe] ratios.Different star formation timescales are proposed to explain thecorrelation between Mg and C abundances. We also find striking CNoverabundances over the entire GC metallicity range. It is interestingto note that the behavior of C and N in metal-poor GCs clearly deviatesfrom that in MR GCs. In particular, for MR GCs, N increases dramaticallywhile C essentially saturates. This may be interpreted as a consequenceof the increasing importance of the CNO cycle with increasingmetallicity.