Spectroscopy of Globular Clusters in NGC 4472

Abstract

Optical multi-slit spectra have been obtained for 47 globular clusters surrounding the brightest Virgo elliptical NGC 4472 (M49). Including data from the literature, we analyze velocities for a total sample of 57 clusters and present the first tentative evidence for kinematic differences between the red and blue cluster populations which make up the bimodal colour distribution of this galaxy. The redder clusters are more centrally concentrated and have a velocity dispersion of 240 km/sec compared with 320 km/sec for the blue clusters. The origin of this difference appears to be a larger component of systematic rotation in the blue cluster system. The larger rotation in the more extended blue cluster system is indicative of efficient angular momentum transport, as provided by galaxy mergers. Masses estimated from the globular cluster velocities are consistent with the mass distribution estimated from X-ray data, and indicate that the M/L rises to 50 times solar at 2.5 R_e.