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arXiv · astro-ph/0210248

Obscured AGN from the ELAIS Deep X-ray Survey

C. J. Willott·C. Simpson·O. Almaini·J. C. Manners·O. Johnson·A. Lawrence·J. S. Dunlop·R. J. Ivison·S. Rawlings·E. Gonzalez-Solares·I. Perez-Fournon·S. Serjeant·S. J. Oliver·N. D. Roche·R. G. Mann·M. Rowan-Robinson
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Abstract

The sources discovered in deep hard X-ray surveys with 2-8 keV fluxes of 10^-14 erg cm^-2 s^-1 make up the bulk of the X-ray background at these energies. We present here detailed multi-wavelength observations of three such sources from the ELAIS Deep X-ray Survey. The observations include sensitive near-infrared spectroscopy with the Subaru Telescope and X-ray spectral information from the Chandra X-ray Observatory. The sources observed all have optical-to-near-IR colours redder than an unobscured quasar and comprise a reddened quasar, a radio galaxy and an optically-obscured AGN. The reddened quasar is at a redshift z=2.61 and shows a very large X-ray absorbing column of N_H approx 3.10^23 cm^-2. This contrasts with the relatively small amount of dust reddening, implying a gas-to-dust ratio along the line-of-sight a hundred times greater than that of the Milky Way. The radio galaxy at z=1.57 shows only narrow emission lines, but has a surprisingly soft X-ray spectrum. The softness of this spectrum either indicates an unusually low gas-to-dust ratio for the absorbing medium or X-ray emission related to the young radio source. The host galaxy is extremely red (R-K=6.4) and its optical/near-IR spectrum is best fit by a strongly reddened (A_V~2) starburst. The third X-ray source discussed is also extremely red (R-K=6.1) and lies in a close grouping of three other R-K>6 galaxies. No emission or absorption lines were detected from this object, but its redshift (and that of one of the nearby galaxies) are constrained by SED-fitting to be just greater than z=1. The extremely red colours of these two galaxies can be accounted for by old stellar populations. These observations illustrate the diverse properties of hard X-ray selected AGN.

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C. J. Willott, C. Simpson, O. Almaini, J. C. Manners, O. Johnson, A. Lawrence, J. S. Dunlop, R. J. Ivison, S. Rawlings, E. Gonzalez-Solares, I. Perez-Fournon, S. Serjeant, S. J. Oliver, N. D. Roche, R. G. Mann, M. Rowan-Robinson. 2002-10-10. Obscured AGN from the ELAIS Deep X-ray Survey. https://doi.org/10.1046/j.1365-8711.2003.06192.x

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