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MC2: boosted AGN and star formation activity in CIZA J2242.8 5301, a massive post-merger cluster at z = 0.19

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Abstract

  • Cluster mergers may play a fundamental role in the formation and evolution of cluster galaxies. Stroe et al. revealed unexpected overdensities of candidate Ha emitters near the ˜1-Mpc-wide shock fronts of the massive (˜2 × 1015 M?) `Sausage' merging cluster, CIZA J2242.8 5301. We used the Keck/Deep Imaging Multi-Object Spectrograph and the William Herschel Telescope/AutoFib2 WYFFOS to confirm 83 Ha emitters in and around the merging cluster. We find that cluster star-forming galaxies in the hottest X-ray gas and/or in the cluster subcores (away from the shock fronts) show high [S II]6716/[S II]6761 and high [S II] 6716/Ha, implying very low electron densities () `Sausage' merging cluster, CIZA J2242.8 5301. We used the Keck/Deep Imaging Multi-Object Spectrograph and the William Herschel Telescope/AutoFib2 WYFFOS to confirm 83 Ha emitters in and around the merging cluster. We find that cluster star-forming galaxies in the hottest X-ray gas and/or in the cluster subcores (away from the shock fronts) show high [S II]6716/[S II]6761 and high [S II] 6716/Ha, implying very low electron densities (-1), likely driven by supernovae. Strong outflows are also found for the cluster Ha active galactic nucleus (AGN). Ha star-forming galaxies in the merging cluster follow the z ˜ 0 mass-metallicity relation, showing systematically higher metallicity (˜0.15-0.2 dex) than Ha emitters outside the cluster (projected R > 2.5 Mpc). This suggests that the shock front may have triggered remaining metal-rich gas which galaxies were able to retain into forming stars. Our observations show that the merger of impressively massive (˜1015 M?) clusters can provide the conditions for significant star formation and AGN activity, but, as we witness strong feedback by star-forming galaxies and AGN (and given how massive the merging cluster is), such sources will likely quench in a few 100 Myr.

Publication Date

  • 2015