Volume 431, Number 1, February III 2005
|Page(s)||87 - 95|
|Published online||02 February 2005|
Looking for obscured QSOs in the X-ray emitting ERO population
Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy e-mail: [paola;rdc;braito;saracco;marcella]@brera.mi.astro.it
2 Universitäts-Sternwarte München, Scheiner Str. 1, 81679 München, Germany e-mail: [bender;feulner;hopp]@usm.uni-muenchen.de
3 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrae, 85748 Garching, Germany e-mail: [bender;hopp;maraston]@mpe.mpg.de
4 University of Texas at Austin, Austin, Texas 78712, USA e-mail: email@example.com
5 IRA - CNR, Firenze, Italy e-mail: firstname.lastname@example.org
Accepted: 7 October 2004
We present XMM-Newton data centered on one of the MUNICS Near Infrared Cluster Survey fields (S2F1) and we discuss the X-ray properties of the 6 X-ray emitting EROs found. For one of them we have already obtained the redshift using near-infrared spectroscopic data, while for the remaining 5 EROs the analysis is based on photometric redshifts. We find evidence for the presence of an X-ray obscured QSO in at least 5 out of the 6 X-ray emitting EROs. For these 5 objects we derive intrinsic (2–10 keV) luminosities in excess of 1044 erg s-1 and intrinsic column densities higher than 1022 cm-2. These values have been obtained through a basic X-ray spectral analysis for the three brightest sources and through the analysis of the hardness ratios for the remaining two. All of these 5 X-ray emitting EROs appear extended in the optical/near-infrared bands indicating that the host galaxy emission dominates at these wavelengths. This suggests that the hosted AGNs are likely to be absorbed also in the optical/near-infrared bands: i.e. they are likely X-ray obscured possible type 2 QSOs. For the remaining ERO the presence of an AGN is suggested both by its high 0.5–2 keV luminosity ( erg s-1) and by its X-ray-to-optical flux ratio. In this case the quality of the present data prevents us from placing firm constraints on the AGN type hosted. Finally, the near-IR spectrum obtained for one of the 6 EROs classifies the host galaxy as an elliptical at with a stellar mass well in excess of 1011 . This result corroborates the possible link between the QSO activity and the formation of massive spheroids.
Key words: galaxies: active / X-rays: galaxies
© ESO, 2005
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