Mon. Not. R. Astron. Soc., 438, 1377-1390 (2014/February-3)
The role of cluster mergers and travelling shocks in shaping the Hα luminosity function at z ∼ 0.2: `sausage' and `toothbrush' clusters.
STROE A., SOBRAL D., ROTTGERING H.J.A. and VAN WEEREN R.J.
Abstract (from CDS):
The most extreme cluster mergers can lead to massive cluster-wide travelling shock waves. 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 Hα luminosity function, using custom-made narrow-band filters matching the cluster redshifts mounted on the Isaac Newton Telescope. We surveyed ∼ 0.28deg2 for each cluster and found 181 line emitters in the `sausage' (volume of 3.371x103Mpc3 for Hα at z = 0.1945) and 141 in the `toothbrush' (4.546x103Mpc3 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, 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 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.