Gemini/GMOS spectra of globular clusters in the Virgo giant elliptical NGC 4649
Forbes, Duncan A.; Beasley, Michael A.; Zepf, Stephen E.; Gebhardt, Karl; Sharples, Ray; Pierce, Michael; Bridges, Terry; Proctor, Robert; Faifer, Favio Raul; Forte, Juan Carlos; Hanes, David A.
Australia, Canada, United States, Argentina, United Kingdom
Abstract
NGC 4649 (M60) is one of a handful of giant Virgo ellipticals. We have obtained Gemini/GMOS (Gemini North Multi-Object Spectrograph) spectra for 38 globular clusters (GCs) associated with this galaxy. Applying the multi-index χ2 minimization technique of Proctor and Sansom with the single stellar population models of Thomas, Maraston and Korn, we derive ages, metallicities and α-element abundance ratios. We find several young (2-3 Gyr old) supersolar metallicity GCs, while the majority are old (>10 Gyr), spanning a range of metallicities from solar to [Z/H]=-2. At least two of these young GCs are at large projected radii of 17-20 kpc. The galaxy itself shows no obvious signs of a recent starburst, interaction or merger. A trend of decreasing α-element ratio with increasing metallicity is found.