Abstract
Abell 2256 is a nearby (z ≈ 0.06), rich cluster of galaxies with fascinating observed properties across a range of wavelengths. Long believed to represent a cluster merger, recent X-ray and optical results have suggested that in addition to primary cluster and subcluster there is evidence for a third, poorer system. We present wide-field high-sensitivity 1.4 GHz VLA radio observations of Abell 2256 in conjunction with optical imaging and additional spectroscopy. Over 40 cluster radio galaxies are identified, with optical spectroscopy indicating emission source (star formation or active galactic nucleus) for most of them. While overall fraction of galaxies exhibiting radio emission is consistent with a large sample of other nearby clusters, we find an increase in activity level of galaxies belonging to third system (hereafter the Group). Specifically, Group has relatively more star formation than both primary cluster and main subcluster. The position of Group is also coincident with observed cluster radio relic. We suggest that Group recently (~0.3 Gyr) merged with primary cluster and that this merger, not ongoing merger of primary and main subcluster, might be responsible for many of unusual radio properties of Abell 2256. Furthermore, greater star formation activity of Group suggests that infall of groups is an important driver of galaxy evolution in clusters.
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