An X-ray bright ERO hosting a type 2 QSO

¹ INAF – Osservatorio Astronomico di Brera (OAB), via Brera 28, 20121 Milano, Italy e-mail: [paola;caccia;braito;rdc;tommaso;saracco]@brera.mi.astro.it
² Exploration of the Universe Division, NASA Goddard Space Flight Center, Greenbelt Road, Greenbelt, MD 20771, USA e-mail: vale@milkyway.gsfc.nasa.gov
³ Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, HI 96720, USA e-mail: akiyama@subaru.naoj.org
⁴ Instituto de Fisica de Cantabria (CSIC-UC), Avenida de los Castros, 39005 Santander, Spain e-mail: [carreraf;ceballos]@ifca.unican.es
⁵ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK e-mail: mjp@mssl.ucl.ac.uk
⁶ X-ray Astronomy Group, Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK e-mail: mgw@star.le.ac.uk

Received: 29 July 2005
Accepted: 4 February 2006

Abstract

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 ( erg s^-1 cm^-2) extremely red objects () 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 ( cm^-2) QSO ( 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 Kα line at 6.4 keV, a first estimate of the redshift of the source is derived (). The presence of a high redshift QSO2 has been finally confirmed through dedicated VLT optical spectroscopic observations (). 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.