The old globular cluster system of NGC 4365: new VLT/FORS2 spectra

Abstract

We present new spectroscopic observations of a sample of globular clusters (GCs) in the Virgo Cluster elliptical NGC4365. The great majority of the objects analysed here, overlap on purpose with objects presented in two previous studies that came to contradictory conclusions. We measure Lick indices for the GCs and infer ages, abundances and alpha-enhancement values by comparing to population synthesis models. Our results do not support the existence of numerous intermediate-age GCs in this galaxy as suggested by some of the past studies. Instead, we find ages, consistent with the range ~8-14 Gyrs (model dependent and with large uncertainties). We also find that the newly observed GCs have [Fe/H]\sim-1.3 to 0.3 dex and the majority are consistent with [alpha/Fe]\sim0.3 dex, independent of metallicity. By comparing the metal sensitive index [MgFe] with optical colours, we find that our data is consistent with 14Gyr models. However for optical/near-infrared colours we find that the same models would have to be redder by ~0.2 mag in order to be consistent with our data. This offset is not found to be consistent with an age effect as it is even larger for younger models.

accepted by MNRAS, 11 pages, 10 figures, 4 tables

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