Merging history of three bimodal clusters^⋆,⋆⋆

¹ Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, UMR 6202 Cassiopée, BP 4229, 06304 Nice Cedex 4, France
e-mail: Sophie.Maurogordato@oca.eu
² CEA, DSM, Irfu, Service d’Astrophysique, C.E. Saclay, 91191 Gif-sur-Yvette Cedex, France
³ Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica, 1, 00133 Roma, Italy
⁴ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁵ ONERA, Optics Department, BP 72, 92322 Chatillon Cedex, France
⁶ CNES, 18 avenue Édouard Belin, 31401 Toulouse Cedex 09, France

Received: 12 March 2010
Accepted: 20 August 2010

Abstract

We present a combined X-ray and optical analysis of three bimodal galaxy clusters selected as merging candidates at z ~ 0.1. These targets are part of MUSIC (MUlti-Wavelength Sample of Interacting Clusters), which is a general project designed to study the physics of merging clusters by means of multi-wavelength observations. Observations include spectro-imaging with XMM-Newton EPIC camera, multi-object spectroscopy (260 new redshifts), and wide-field imaging at the ESO 3.6 m and 2.2 m telescopes. We build a global picture of these clusters using X-ray luminosity and temperature maps together with galaxy density and velocity distributions. Idealized numerical simulations were used to constrain the merging scenario for each system. We show that A2933 is very likely an equal-mass advanced pre-merger  ~200 Myr before the core collapse, while A2440 and A2384 are post-merger systems (~450 Myr and  ~1.5 Gyr after core collapse, respectively). In the case of A2384, we detect a spectacular filament of galaxies and gas spreading over more than 1   h^-1 Mpc, which we infer to have been stripped during the previous collision. The analysis of the MUSIC sample allows us to outline some general properties of merging clusters: a strong luminosity segregation of galaxies in recent post-mergers; the existence of preferential axes – corresponding to the merging directions – along which the BCGs and structures on various scales are aligned; the concomitance, in most major merger cases, of secondary merging or accretion events, with groups infalling onto the main cluster, and in some cases the evidence of previous merging episodes in one of the main components. These results are in good agreement with the hierarchical scenario of structure formation, in which clusters are expected to form by successive merging events, and matter is accreted along large-scale filaments.