Gemini/GMOS Spectroscopy of Globular Clusters in the Merger Remnant Galaxy M85

Abstract

M85 is a peculiar S0 galaxy in Virgo and is a well-known merger remnant. In this paper, we present the first spectroscopic study of globular clusters (GCs) in M85. We obtain spectra for 21 GC candidates and the nucleus of M85 using the Gemini Multi-Object Spectrograph on the Gemini North 8.1 m telescope. From their radial velocities, 20 of the GCs are found to be members of M85. We find a strong rotation signal of the M85 GC system with a rotation amplitude of 235 km s${}^{-1}$. The rotation axis of the GC system has a position angle of about 161${}^{\circ }$, which is 51$\text{.}{}^{\circ }$5 larger than that of the stellar light. The rotation-corrected radial velocity dispersion of the GC system is estimated to be ${\sigma }_{\mathrm{r},\mathrm{cor}}=$ 160 km s${}^{-1}$. The rotation parameter $\Omega R_{\mathrm{icor}}/{\sigma }_{\mathrm{r},\mathrm{cor}}$ of the GC system is derived to be 1.47${}_{-0.48}^{+1.05}$, which is one of the largest among known early-type galaxies. The ages and metallicities of the GCs, which show the same trend as the results based on Lick indices, are derived from full spectrum fitting (ULySS). About a half of the GCs are an intermediate-age population of which the mean age is $\sim$ 3.7 $\pm$ 1.9 Gyr, having a mean [Fe/H] value of --0.26. The other half are old and metal-poor. These results suggest that M85 experienced a wet merging event about 4 Gyr ago, forming a significant population of star clusters. The strong rotational feature of the GC system can be explained by an off-center major merging.

20 pages, 13 figures, 7 tables, accepted for publication in ApJ

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• A Wide-field Photometric Survey of Globular Clusters in the Peculiar Early-type Galaxy M85
• The complex globular cluster system of the S0 galaxy NGC 4382 in the outskirts of the Virgo Cluster
• The Next Generation Virgo Cluster Survey. XXXIII. Stellar Population Gradients in the Virgo Cluster Core Globular Cluster System
• Property of Young Massive Clusters in a Galaxy-Galaxy Merger Remnant
• Initial Mass Function Variation in two Elliptical Galaxies using Near-Infrared Tracers
• Age-Divided Mean Stellar Populations from Full Spectrum Fitting as the Simplified Star Formation and Chemical Evolution History of a Galaxy: Methodology and Reliability
• Globular Cluster Systems and X-Ray Atmospheres in Galaxies
• Mysterious Globular Cluster System of the Peculiar Massive Galaxy M85
• Properties of Globular Clusters in Galaxy Clusters: Sensitivity from the Formation and Evolution of Globular Clusters