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arXiv · 1503.07244

On the Merging Cluster Abell 578 and Its Central Radio Galaxy 4C +67.13

K. Hagino·L. Stawarz·A. Siemiginowska·C. C. Cheung·D. Koziel-Wierzbowska·A. Szostek·G. Madejski·D. E. Harris·A. Simionescu·T. Takahashi
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Abstract

Here we analyze radio, optical, and X-ray data for a peculiar cluster Abell 578. This cluster is not fully relaxed and consists of two merging sub-systems. The brightest cluster galaxy, CGPG 0719.8+6704, is a pair of interacting ellipticals with projected separation $\sim$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 $\sim10^{-4}$ (for the estimated black hole masses of $\sim 3 \times 10^8\,M_\odot$ and $\sim 10^9 \, M_\odot$). The gathered X-ray ({\it 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 ($\sim 60$\,kpc projected) between the position of the brightest cluster galaxy 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 $\sim 1.4$) and heated (from $\simeq 2.0$\,keV up to 2.7\,keV), consistent with the presence of a weak shock (Mach number $\sim 1.3$) driven by the expanding jet cocoon. This would then require the jet kinetic power of the order of $\sim 10^{45}$\,erg\,s$^{-1}$, 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.

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K. Hagino, L. Stawarz, A. Siemiginowska, C. C. Cheung, D. Koziel-Wierzbowska, A. Szostek, G. Madejski, D. E. Harris, A. Simionescu, T. Takahashi. 2015-03-25. On the Merging Cluster Abell 578 and Its Central Radio Galaxy 4C +67.13. https://doi.org/10.1088/0004-637x%2F805%2F2%2F101

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