VLT Spectroscopy of NGC 3115 Globular Clusters

Abstract.

We present results derived from VLT-FORS2 spectra of 17 globular clusters associated with the nearby lenticular galaxy NGC3115. Comparing line-strength indices to new stellar population models by Thomas et al. we determine ages, metallicities and element abundance ratios. Our data are also compared with the Lick/IDS observations of Milky Way and M 31 globular clusters. Our best age estimates show that the observed clusters which sample the bimodal colour distribution of NGC 3115 globular clusters are coeval within our observational errors (2-3 Gyr). Our best calibrated age/metallicity diagnostic diagram (H$\beta\ vs$ [MgFe]) indicates an absolute age of 11-12 Gyr consistent with the luminosity weighted age for the central part of NGC 3115. We confirm with our accurate line-strength measurements that the (V-I) colour is a good metallicity indicator within the probed metallicity range (-1.5 < [Fe/H] < 0.0). The abundance ratios for globular clusters in NGC3115 give an inhomogeneous picture. We find a range from solar to super-solar ratios for both blue and red clusters. This is similar to the data for M 31 while the Milky Way seems to harbour clusters which are mainly consistent with [$\alpha$/Fe] $\simeq 0.3$.