Dynamics of the NGC 4636 Globular Cluster System

Abstract

NGC4636, a giant elliptical in the Virgo Southern Extension at a distance of 15Mpc [10] has some outstanding properties. Its specific frequency of globular clusters is unusually high [4],[2]. Far-infrared emission points to a considerable amount of warm dust, perhaps supplied in a recent merger event [9]. Moreover, it exhibits a bright X-ray halo [7],[3] which extends out to a radius of 300 kpc. Both ASCA [7] and Chandra [6] data have been used to infer an extremely dark matter dominated total mass. However, other work based on Chandra observations [3] interpret the strong X-ray emission as being due to a transient period of a high cooling rate, rendering the derivation of the mass profile doubtful. Here, we present the first dynamical study of the NGC4636 globular cluster system (GCS). We use the radial velocities of 176 globular clusters (GCs) in the range 4–70 kpc, the overwhelming majority being within 30 kpc, to derive a mass profile by stellar dynamical means.