Spectral and morphological signatures of cluster merger shocks: CIZA J2242.8+5301

A. Stroe1*, R. van Weeren2, D. Sobral1,3, C. Rumsey4, H. Intema5, H. Röttgering1, J. Harwood6, R. Saunders4,7, M. Brüggen8 and M. Hoeft9
1Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands
2Harvard Smithsonian Center for Astrophysics (CfA - SAO), 60 Garden Street Cambridge, MA 02138
3CAAUL, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1359-018, Lisboa, Portugal
4Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE
5NRAO, Pete V. Domenici Science Operations Center, 1003 Lopezville Road, Socorro, NM 87801-0387, USA
6University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
7Kavli Institute for Cosmology Cambridge, Madingley Road, Cambridge CB3 0HA, UK
8Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
9Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778, Tautenburg, Germany

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The CIZA J2242.8+5301 cluster hosts an extraordinary, narrow, Mpc-wide, diffuse patch of radio emission tracing travelling shock waves, called a relic. We perform a multi-wavelength of observations of the cluster. We discover radio spectral steepening and increasing spectral curvature in the shock downstream area, indicative of emission produced by spectrally-aged electrons, following a JP ageing model. The curved integrated spectrum towards 16 GHz challenges the favoured relic formation model. Further, we find a boosting the number density of Hα emitters by a factor of 10, possibly caused by interactions of the galaxies with the shock wave.

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Keywords : Galaxies: Clusters: general, intracluster medium, individual: CIZA J2242.8+5301 – Galaxies: luminosity function