Radio morphology and spectral analysis of cD galaxies in rich and poor galaxy clusters

¹ INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy e-mail: tventuri@ira.inaf.it
² INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40126 Bologna, Italy
³ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40126 Bologna, Italy
⁴ INAF – Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra, Italy
⁵ Tata Institute of Fundamental Research, National Centre for Radio Astrophysics, Ganeshkhind, Pune 411 007, India
⁶ Dipartimento di Fisica, Universitá di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁷ Harvard-Smithsonian Centre for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received: 21 May 2007
Accepted: 21 August 2007

Abstract

Aims.We present a radio morphological study and spectral analysis of a sample of 13 cD galaxies in rich and poor clusters of galaxies.

Methods.Our study is based on new high sensitivity Giant Metrewave Radio Telescope (GMRT) observations at 1.28 GHz, 610 MHz and 235 MHz, and on archival data. From a statistical sample of cluster cD galaxies we selected those sources with little information available in the literature and promising for the detection of aged radio emission. As well as the high sensitivity images for all 13 radio galaxies, we present also a detailed spectral analysis for 7 of them.

Results.We found a variety of morphologies and linear sizes, as typical for radio galaxies in the radio power range sampled here (low to intermediate power radio galaxies). The spectral analysis shows that 10/13 radio galaxies have a steep radio spectrum, with spectral index α ≥ 1. In general, the radiative ages and growth velocities are consistent with previous findings that the evolution of radio galaxies at cluster centres is affected by the dense external medium (i.e. low growth velocities and old ages). We suggest that the dominant galaxies in A 2622 and MKW 03s are dying radio sources, which at present are not fed by nuclear activity. On the other hand, the spectacular source at the centre of A 2372 might be a very interesting example of a restarted radio galaxy. For this source we estimated a life cycle of the order of 10⁶ yr.