Star clusters in the interacting galaxy system Arp 284

Abstract

We present results from a study of proto-globular cluster candidates in the interacting galaxy system Arp 284 (NGC 7714/5) using data from the Hubble Space Telescope. Previous studies of the Antennae and M51 have suggested that the majority of young massive star clusters dissolve within 20 Myr due to mass loss. We use the evolutionary synthesis code Starburst99 to estimate ages and extinctions for approximately 175 clusters visible with HST. We also use lower-resolution GALEX and ground-based H-alpha data to estimate the ages of the giant HII regions in which these clusters are found, and compare the Spitzer colours of these HII regions to those of star forming regions in other interacting systems. The ages are also used to aid in the interpretation of Chandra X-ray data. Clusters in the tidal tails of NGC 7714 are generally found to have ages less than 20 Myr, though observational limits make the significance of this result uncertain. Older clusters, though not numerous, have nearly the same spatial distribution within the imaged portion of NGC 7714 as young clusters. The cluster population in the bridge connecting the two galaxies appears to be older, but the data in this part of the system is too limited to draw firm conclusions. The ages of the giant HII regions in NGC 7714 are generally older than those of their constituent clusters, possibly indicating that the young clusters we detect are surrounded by their dispersed predecessors.