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The role of cluster mergers and travelling shocks in shaping the Hα luminosity function at z ~ 0.2: 'sausage' and 'toothbrush' clusters

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  • Andra Stroe
  • David Sobral
  • Huub J. A. Röttgering
  • Reinout J. van Weeren
Article numberstt2286
<mark>Journal publication date</mark>21/02/2014
<mark>Journal</mark>Monthly Notices of the Royal Astronomical Society
Issue number2
Number of pages14
Pages (from-to)1377-1390
Publication StatusPublished
Early online date27/12/13
<mark>Original language</mark>English


Themost extreme clustermergers can lead to massive cluster-wide travelling shockwaves. The CIZA J2242.8+5301 ('sausage') and 1RXS J0603.3+4213 ('toothbrush') clusters (z ~ 0.2) host enormous radio-emitting shocks with simple geometry. We investigate the role of mergers and shocks in shaping the Ha luminosity function, using custom-made narrow-band filters matching the cluster redshifts mounted on the Isaac Newton Telescope. We surveyed ~0.28 deg2 for each cluster and found 181 line emitters in the 'sausage' (volume of 3.371 × 103 Mpc3 for Hα at z = 0.1945) and 141 in the 'toothbrush' (4.546 × 103 Mpc3 for Hα at z = 0.225), out of which 49 ('sausage') and 30 ('toothbrush') are expected to be Hα. We build luminosity functions for the field-of-view down to an average limiting star formation rate of 0.14M yr-1, find good agreement with field luminosity functions at z = 0.2, but significant differences between the shapes of the luminosity functions for the two clusters. We discover extended, tens-of-kpc-wide Hα haloes in galaxies neighbouring relics, which were possibly disrupted by the passage of the shock wave. By comparing the 'sausage' cluster with blank fields and other clusters, we also uncover an order of magnitude boost (at 9σ level) in the normalization f φ* of the luminosity function in the relic areas. Our results suggest that cluster mergers may play an important role in the evolution of cluster galaxies through shock-induced star formation.