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MC<sup>2</sup>: Boosted AGN and star formation activity in CIZA J2242.8+5301, a massive post-merger cluster at z = 0.19

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  • David Sobral
  • Andra Stroe
  • William A. Dawson
  • David Wittman
  • M. James Jee
  • Huub Röttgering
  • Reinout J. van Weeren
  • Marcus Brüggen
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<mark>Journal publication date</mark>11/06/2015
<mark>Journal</mark>Monthly Notices of the Royal Astronomical Society
Issue number1
Volume450
Number of pages16
Pages (from-to)630-645
Publication StatusPublished
Early online date23/04/15
<mark>Original language</mark>English

Abstract

Cluster mergers may play a fundamental role in the formation and evolution of cluster galaxies. Stroe et al. revealed unexpected overdensities of candidate Hα emitters near the ~1-Mpc-wide shock fronts of the massive (~2 × 10<sup>15</sup> M<inf>⊙</inf>) '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 Hα 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/Hα, implying very low electron densities (<30 × lower than all other star-forming galaxies outside the cluster) and/or significant contribution from supernovae, respectively. All cluster star-forming galaxies near the cluster centre show evidence of significant outflows (blueshifted Na D ~200-300 km s<sup>-1</sup>), likely driven by supernovae. Strong outflows are also found for the cluster Hα active galactic nucleus (AGN). Hα star-forming galaxies in the merging cluster follow the z ~ 0 mass-metallicity relation, showing systematically higher metallicity (~0.15-0.2 dex) than Hα 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 (~10<sup>15</sup> M<inf>⊙</inf>) 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.