Newly Identified Star Clusters in NGC 6822, and the Age Distribution of Its Cluster System

Abstract

From past ground-based imaging and our current Hubble Space Telescope images, we have identified 51 candidate open clusters in the dwarf irregular galaxy NGC 6822. Of these, 25 candidates are located on our HST images with standard wideband filters, 16 of which are securely identified as true clusters. Integrated photometry in B, V, and I for seven clusters, and in V and I for eight clusters, was performed on the HST images. We present integrated magnitudes and colors for these clusters and compare their color-magnitude and two-color diagrams with those of cluster systems of other galaxies. We derive rough age estimates and the cluster formation rate and discuss the age distribution in terms of the cluster disruption rate. The cluster-specific frequency is intermediate between that of cluster-rich galaxies such as the LMC and a first look at cluster-poor galaxies such as IC 1613.

Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is owned and operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.