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An X-ray bright ERO hosting a type 2 QSO

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posted on 2012-10-24, 09:05 authored by P. Severgnini, A. Caccianiga, V. Braito, Della Ceca R, T. Maccacaro, P. Saracco, M. Akiyama, F. J. Carrera, M. T. Ceballos, M. J. Page, M. G. Watson
We present the XMM-Newton and the optical-VLT spectra along with the optical and the near-infrared photometric data of one of the brightest X-ray ( $F_{2{-}10~\rm keV}\sim10^{-13}$ erg s-1 cm-2) extremely red objects ($R-K\ge5$) discovered so far. The source, XBS J0216-0435, belongs to the XMM-Newton Bright Serendipitous Survey and it has extreme X-ray-to-optical (~220) and X-ray-to-near-infrared (~60) flux ratios. Thanks to its brightness, the X-ray statistics are good enough for an accurate spectral analysis by which the presence of an X-ray obscured ( $N_{\rm H}>10^{22}$ cm-2) QSO ( $L_{2{-}10~\rm keV}=4\times10^{45}$ erg s-1) is determined. A statistically significant (~99%) excess around 2 keV in the observed-frame suggests the presence of an emission line. By assuming that this feature corresponds to the iron K$\alpha$ line at 6.4 keV, a first estimate of the redshift of the source is derived ( $z_{\rm X}\sim2$). The presence of a high redshift QSO2 has been finally confirmed through dedicated VLT optical spectroscopic observations ( $z_{\rm O}=1.985\pm0.002$). This result yields to an optical validation of a new X-ray Line Emitting Object (XLEO) for which the redshift has been firstly derived from the X-ray data. XBS J0216-0435 can be considered one of the few examples of X-ray obscured QSO2 at high redshift for which a detailed X-ray and optical spectral analysis has been possible. The spectral energy distribution from radio to X-rays is also presented. Finally from the near-infrared data the luminosity and the stellar mass of the host galaxy has been estimated finding a new example of the coexistence at high-z between massive galaxies and powerful QSOs.



Astronomy & Astrophysics, 2006, 451 (3), pp. 859-864


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