Multiwavelength observations of serendipitous Chandra X-ray sources in the field of A 2390 |
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| Authors: | C S Crawford P Gandhi A C Fabian R J Wilman R M Johnstone A J Barger † L L Cowie ‡ |
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| Institution: | Institute of Astronomy, Madingley Road, Cambridge CB3 0HA; Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands; Institute for Astronomy, 2680 Woodlawn Drive, Honolulu HI 96822, USA; Department of Astronomy, University of Wisconsin-Madison, 475 N Charter Street, Madison, WI 53706, USA |
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| Abstract: | We present optical spectra and near-infrared imaging of a sample of 31 serendipitous X-ray sources detected in the field of Chandra observations of the A 2390 cluster of galaxies. The sources have 0.5–7 keV fluxes of (0.6–8)×10-14 erg cm-2 s-1 and lie around the break in the 2–10 keV source counts. They are therefore typical of sources dominating the X-ray Background in that band. 12 of the 15 targets for which we have optical spectra show emission lines at a range of line luminosities, and half of these show broad lines. These active galaxies and quasars have soft X-ray spectra. Including photometric redshifts and published spectra, we have redshifts for 17 of the sources, ranging from z ～0.2 up to z ～3 , with a peak between z =1–2 . 10 of our sources have hard X-ray spectra indicating a spectral slope flatter than that of a typical unabsorbed quasar. Two hard sources that are gravitationally lensed by the foreground cluster are obscured quasars, with intrinsic 2–10 keV luminosities of (0.2–3)×1045 erg s-1 , and absorbing columns of N H>1023 cm-2 . Both of these sources were detected in the mid-infrared by ISOCAM on the Infrared Space Observatory , which when combined with radiative transfer modelling leads to the prediction that the bulk of the reprocessed flux emerges at ～100 μm. |
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| Keywords: | galaxies: active diffuse radiation infrared: galaxies X-rays: galaxies |
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