Volume 409, Number 1, October I 2003
|Page(s)||65 - 78|
|Published online||17 November 2003|
The HELLAS2XMM survey*
III. Multiwavelength observations of hard X–ray selected sources in the PKS 0312–77 field
Dipartimento di Astronomia Università di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: email@example.com
2 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: comastri,mignoli,firstname.lastname@example.org
3 INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy e-mail: fiore,email@example.com
4 Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA e-mail: firstname.lastname@example.org
5 INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy e-mail: email@example.com
6 Dipartimento di Fisica Università di Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy e-mail: lafranca,matt,firstname.lastname@example.org
7 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy e-mail: email@example.com
8 IASF – CNR, Istituto di Fisica Cosmica, via Bassini 15, 20133, Milano, Italy e-mail: baldi,firstname.lastname@example.org
Corresponding author: M. Brusa, email@example.com
Accepted: 11 July 2003
We present extensive optical, radio and infrared follow-up observations of a sample of 35 hard X–ray (2–10 keV) selected sources discovered serendipitously in the PV XMM–Newton observation of the radio–loud quasar PKS 0312–77 field, for which also an archival Chandra observation is available. The observations have been carried out as part of the HELLAS2XMM survey, a program aimed to understand the nature of the sources responsible for the bulk of the hard X–ray Background (XRB). The identification of the optical counterparts greatly benefits from the positional accuracy obtained from Chandra and radio observations. As a consequence, the spectroscopic completeness of the present sample (80%) is limited only by the faintness of the optical counterparts. The multiwavelength coverage of our survey allows us to unveil a large spread in the overall properties of hard X–ray selected sources. At low redshift (), the source breakdown includes Broad Line AGN, Narrow Emission–Line Galaxies, and optically “normal” galaxies. All the ten sources at are spectroscopically classified as Broad Line AGNs. A few of them show significant intrinsic X–ray absorption ( cm-2), further supporting previous evidence of a decoupling between optical and X–ray properties at high luminosities and redshifts. Finally, a non negligible fraction (~15%) of the hard X–ray sources are not detected down to the limiting magnitude of the optical images. The corresponding high X–ray to optical flux ratio, X–ray and optical–infrared colors strongly suggest that they are high redshift, obscured AGN.
Key words: surveys / galaxies: active / X-ray: galaxies / X–rays: general / X–rays: diffuse background
This work is based on observations collected at the European Southern Observatory, La Silla, Chile (proposals ID: 66.A-0520(A), 67.A-0401(A), 68.A-0514(A)) and Paranal, Chile (proposal ID: 69.A-0506(A)), and observations made with the XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA)
© ESO, 2003
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