Internal dynamics of Abell 2294: a massive, likely merging cluster

¹ Dipartimento di Fisica dell' Università degli Studi di Trieste – Sezione di Astronomia, via Tiepolo 11, 34143 Trieste, Italy e-mail: girardi@oats.inaf.it
² INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
³ Fundación Galileo Galilei – INAF, Rambla José Ana Fernández Perez 7, 38712 Breña Baja (La Palma), Canary Islands, Spain
⁴ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna (Tenerife), Canary Islands, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, Av. del Astrofísico Franciso Sánchez s/n, 38205 La Laguna (Tenerife), Canary Islands, Spain

Received: 22 January 2010
Accepted: 18 April 2010

Abstract

Context. The mechanisms giving rise to diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated.

Aims. We seek to explore the internal dynamics of the cluster Abell 2294, which has been shown to host a radio halo.

Methods. Our analysis is mainly based on redshift data for 88 galaxies acquired at the Telescopio Nazionale Galileo. We combine galaxy velocities and positions to select 78 cluster galaxies and analyze its internal dynamics. We also use both photometric data acquired at the Isaac Newton Telescope and X-ray data from the Chandra archive.

Results. We re-estimate the redshift of the large, brightest cluster galaxy (BCG) obtaining < z > = 0.1690, which closely agrees with the mean cluster redshift. We estimate a quite large line-of-sight (LOS) velocity dispersion ~ 1400 km sand X-ray temperature T_X ~ 10 keV. Our optical and X-ray analyses detect substructure. Our results imply that the cluster is composed of two massive subclusters separated by a LOS rest frame velocity difference V_rf ~ 2000 km s^-1, very closely projected in the plane of sky along the SE-NW direction. This observational picture, interpreted in terms of the analytical two-body model, suggests that Abell 2294 is a cluster merger elongated mainly in the LOS direction and captured during the bound outgoing phase, a few fractions of Gyr after the core crossing. We find that Abell 2294 is a very massive cluster with a range of M = 2–4 × 10¹⁵ h₇₀^-1 , depending on the adopted model. In contrast to previous findings, we find no evidence of Hα emission in the spectrum of the BCG galaxy.

Conclusions. The emerging picture of Abell 2294 is that of a massive, quite “normal” merging cluster, like many clusters hosting diffuse radio sources. However, perhaps because of its particular geometry, more data are needed for reach a definitive, more quantitative conclusion.