Young Stellar Populations in the Collisional Ring Galaxy NGC 922

Abstract

We studied the star cluster population properties in the nearby collisional ring galaxy NGC 922 using HST/WFPC2 photometry and population synthesis modeling. We found that 69% of the detected clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Halpha emission. The images also show a tidal plume pointing toward the companion. Its stellar age is consistent with pre-existing stars that were probably stripped off during the passage of the companion. We compared the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field. It indicates very similar masses and sizes, suggesting similar origins. Finally, we found clusters that are excellent progenitor candidates for faint fuzzy clusters.