ON THE MERGING CLUSTER ABELL 578 AND ITS CENTRAL RADIO GALAXY 4C+67.13

• Published in: The Astrophysical journal 2015-06, Vol.805 (2), p.1-11, Article 101
• Main Authors: Hagino, K, Stawarz, L, Siemiginowska, A, Cheung, C C, Koziel-Wierzbowska, D, Szostek, A, Madejski, G, Harris, D E, Simionescu, A, Takahashi, T
• Format: Article
• Language: English
• Subjects: Accretion; ASTRO; ASTRONOMY AND ASTROPHYSICS; astrophysics; Asymptotic properties; Clusters; Galactic clusters; galaxies: active; galaxies: clusters: individual (Abell 578); galaxies: individual (4C+67.13); galaxies: jets; GRQC; intergalactic medium; Merging; Radio; Radio galaxies; X-rays; X-rays: galaxies: clusters
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/805/2/101

Here we analyze radio, optical, and X-ray data for the peculiar cluster Abell 578. This cluster is not fully relaxed and consists of two merging sub-systems. The brightest cluster galaxy (BCG), CGPG 0719.8+6704, is a pair of interacting ellipticals with projected separation ~10 kpc, the brighter of which hosts the radio source 4C+67.13. The Fanaroff-Riley type-II radio morphology of 4C+67.13 is unusual for central radio galaxies in local Abell clusters. Our new optical spectroscopy revealed that both nuclei of the CGPG 0719.8+6704 pair are active, albeit at low accretion rates corresponding to the Eddington ratio ~10 super(-4) (for the estimated black hole masses of ~3 x 10 super(8) M sub([middot in circle]) and ~10 super(9) M sub([middot in circle])). The gathered X-ray (Chandra) data allowed us to confirm and to quantify robustly the previously noted elongation of the gaseous atmosphere in the dominant sub-cluster, as well as a large spatial offset (~60 kpc projected) between the position of the BCG and the cluster center inferred from the modeling of the X-ray surface brightness distribution. Detailed analysis of the brightness profiles and temperature revealed also that the cluster gas in the vicinity of 4C+67.13 is compressed (by a factor of about ~1.4) and heated (from [Asymptotically = to]2.0 keV up to 2.7 keV), consistent with the presence of a weak shock (Mach number ~1.3) driven by the expanding jet cocoon. This would then require the jet kinetic power of the order of ~10 super(45) erg s super(-1), implying either a very high efficiency of the jet production for the current accretion rate, or a highly modulated jet/accretion activity in the system.