Chandra observation of the multiple merger cluster Abell 521.pdf

a r X i v : a s t r o - p h / 0 5 0 8 5 8 5 v 2 1 5 S e p 2 0 0 5 Astronomy Astrophysics manuscript no. ferrari˙A521 February 5, 2008 (DOI: will be inserted by hand later) Chandra observation of the multiple merger cluster Abell 521 Ferrari, C.1, Arnaud, M.2, Ettori, S.3, Maurogordato, S.4, and Rho, J.5 1 Institut fu?r Astrophysik, Technikerstra?e 25, 6020 Innsbruck, Austria 2 CEA/DSM/DAPNIA Service d’Astrophysique, CEA Saclay, L’Orme des Merisiers, Ba?t. 709, 91191 Gif-sur- Yvette, France 3 Osservatorio Astronomico di Bologna, Istituto Nazionale di Astrofisica, via Ranzani 1, I-40127 Bologna, Italy 4 Laboratoire Cassiope?e, CNRS/UMR 6202, Observatoire de la Co?te d’Azur, BP 4229, 06304 Nice Cedex 4, France 5 Spitzer Science Center, California Institute of Technology, Pasadena, CA 911251 Received 1 August 2005; accepted 8 September 2005 Abstract. We present the Chandra analysis of the rich galaxy cluster Abell 521 (z=0.247). The high resolution of the Chandra observation has allowed us to refine the original merging scenario proposed for A521, and to reveal new features in its X-ray emission. A521 has strongly substructured ICM density and temperature maps. Its X-ray diffuse emission is elongated along a NW/SE direction (SX2) and shows two major components, a main cluster and a northern group of galaxies. This latter is in turn substructured, showing a clump of cold and very dense gas centred on the Brightest Cluster Galaxy (BCG), and a northern tail aligned in the SX2 direction. A compression of the X-ray isophotes is also observed South of the BCG. We conclude that the northern group is infalling onto the main cluster along the NW/SE direction. This hypothesis is corroborated by the presence of a hot bar in the ICM temperature map located between the southern and northern regions, as the gas could be compressionally heated due to the subclusters’ collision. The hot region corresponds to the eastern part of an over-dense ridge of galaxies, along which it was