Radial Velocities of Newly Discovered Globular Clusters in NGC 5128

Abstract

We present radial velocity measurements for 74 globular clusters (GCs) in the nearby giant elliptical galaxy NGC 5128, of which 31 are newly discovered. All the GC candidates were taken from the list of possible new clusters given in the photometric survey of Harris and coworkers. In addition to the newly confirmed clusters, we identified 24 definite foreground stars and 31 probable background galaxies. From a combined list of 299 known GCs in NGC 5128 with measured radial velocities and metallicity-sensitive (C - T1) photometric indices, we construct a new metallicity distribution function (MDF) for the cluster system. The MDF shows an approximately bimodal form, with centroids at [Fe/H] = -1.46 and -0.53 and with nearly equal numbers of metal-poor and metal-rich clusters in the two modes. However, there are many intermediate-color clusters in the distribution, and the fainter clusters tend to have a higher proportion of redness. These features of the MDF may indicate a widespread age range within the cluster system, as well as an intrinsically broad metallicity spread.