GMOS Spectroscopy of the S0 Galaxy NGC 3115

Abstract

We present Gemini GMOS longslit spectroscopy of the isolated S0 galaxy NGC 3115. We have determined kinematical data and Lick/IDS absorption line-strength indices for the major axis out to around 9 kpc and for the minor axis out to around 5 kpc (around 2Re). Using stellar population models which include the effects of variable [alpha/Fe] ratios we derive metallicities, abundance ratios and ages for the stellar population of NGC 3115. We find that [alpha/Fe] remains fairly constant with increasing radius at around [alpha/Fe] = 0.17 for the major axis but increases rapidly for the minor axis to around [alpha/Fe] = 0.3. We also find that to first order this behaviour can be explained by a simple spheroid + disc model, where the spheroid has [alpha/Fe] = 0.3 and the disc shows close to solar abundance ratios. The disc also appears considerably younger than the spheroid, having an age of around 6 Gyr compared to 12 Gyr for the spheroid. We compare these results to those previously presented for the globular cluster system of NGC 3115.