期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 333, 期 4, 页码 809-824出版社
BLACKWELL PUBLISHING LTD
DOI: 10.1046/j.1365-8711.2002.05454.x
关键词
galaxies : active; diffuse radiation; infrared : galaxies; X-rays : galaxies
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)x10(-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 similar to0.2 up to z similar to3, 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)x10(45) erg s(-1), and absorbing columns of N (H) >10(23) 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 similar to100 mum.
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