Suzaku observations of the type 2 QSO in the central galaxy of the Phoenix cluster

Abstract

We report the \Suzaku/XIS and HXD and \Chandra/ACIS-I results on the X-ray spectra of the Phoenix cluster at the redshift $z=0.596$. The spectrum of the intracluster medium (ICM) is well-reproduced with the emissions from a low temperature ($\sim 3.0$\,keV and $\sim 0.76$\,solar) and a high temperature ($\sim 11$\,keV and $\sim 0.33$\,solar) plasmas; the former is localized at the cluster core, while the latter distributes over the cluster. In addition to these ICM emissions, a strongly absorbed power-law component is found, which is due to an active galactic nucleus (AGN) in the cluster center. The absorption column density and unobscured luminosity of the AGN are $\sim 3.2\times 10^{23}$\,cm${}^{-2}$ and $\sim 4.7\times 10^{45}$\,ergs\,s${}^{-1}$ (2-10\,keV), respectively. Furthermore, a neutral iron (\ion{Fe}{1}) K-shell line is discovered for the first time with the equivalent width (EW) of $\sim 150$\,eV at the rest frame. The column density and the EW of the \ion{Fe}{1} line are exceptionally large for such a high luminosity AGN, and hence the AGN is classified as a type 2 quasi-stellar object (QSO). We speculate that the significant fraction of the ICM cooled gas would be consumed to maintain the torus and to activate the type 2 QSO. The Phoenix cluster has a massive starburst in the central galaxy, indicating suppression in the cooling flow is less effective. This may be because the onset of the latest AGN feedback has occurred recently and it has not yet been effective. Alternatively, the AGN feedback is predominantly in radiative-mode not in kinetic-mode and the torus may work as a shield to reduce its effect.

8 pages, 4 figures, 1 table, accepted for publication in ApJ

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• Deep Chandra, HST-COS, and Megacam Observations of the Phoenix Cluster: Extreme Star Formation and AGN Feedback on Hundred Kiloparsec Scales
• Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the Core of the Phoenix Cluster
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