Open AccessMultiwavelength observations of serendipitous Chandra X‐ray sources in the field of A 2390
Author(s) -
Crawford C. S.,
Gandhi P.,
Fabian A. C.,
Wilman R. J.,
Johnstone R. M.,
Barger A. J.,
Cowie L. L.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05454.x
Subject(s) - physics , astrophysics , quasar , redshift , galaxy , spectral line , observatory , active galactic nucleus , flux (metallurgy) , infrared , astronomy , galaxy cluster , luminous infrared galaxy , emission spectrum , cluster (spacecraft) , materials science , computer science , metallurgy , programming language
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)×10 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 ∼100 μm.