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The XMM deep survey in the CDF-S: VI. Obscured AGN selected as infrared power-law galaxies

Abstract: Context. Accretion onto supermassive black holes is believed to occur mostly in obscured active galactic nuclei (AGN). Such objects are proving rather elusive in surveys of distant galaxies, including those at X-ray energies. Aims. Our main goal is to determine whether the revised IRAC criteria of Donley et al. (2012, ApJ, 748, 142; objects with an infrared (IR) power-law spectral shape), are effective at selecting X-ray type-2 AGN (i.e., absorbed NH > 1022 cm?2). Methods. We present the results from the X-ray spectral analysis of 147 AGN selected by cross-correlating the highest spectral quality ultra-deep XMM-Newton and the Spitzer/IRAC catalogues in the Chandra Deep Field South. Consequently it is biased towards sources with high S/N X-ray spectra. In order to measure the amount of intrinsic absorption in these sources, we adopt a simple X-ray spectral model that includes a power-law modified by intrinsic absorption at the redshift of each source and a possible soft X-ray component. Results. We find 21/147 sources to be heavily absorbed but the uncertainties in their obscuring column densities do not allow us to confirm their Compton-Thick nature without resorting to additional criteria. Although IR power-law galaxies are less numerous in our sample than IR non-power-law galaxies (60 versus 87 respectively), we find that the fraction of absorbed (Nintr H > 1022 cm?2) AGN is significantly higher (at about 3 sigma level) for IR-power-law sources (?2/3) than for those sources that do not meet this IR selection criteria (?1/2). This behaviour is particularly notable at low luminosities, but it appears to be present, although with a marginal significance, at all luminosities. Conclusions. We therefore conclude that the IR power-law method is efficient in finding X-ray-absorbed sources. We would then expect that the long-sought dominant population of absorbed AGN is abundant among IR power-law spectral shape sources not detected in X-rays.

Otras publicaciones de la misma revista o congreso con autores/as de la Universidad de Cantabria

 Autoría: Castelló-Mor N., Carrera F.J., Alonso-Herrero A., Mateos S., Barcons X., Ranalli P., Pérez-González P.G., Comastri A., Vignali C., Georgantopoulos I.,

 Fuente: Astronomy and Astrophysics, 2013, 556, A114

Editorial: EDP Sciences

 Fecha de publicación: 01/08/2013

Nº de páginas: 13

Tipo de publicación: Artículo de Revista

 DOI: 10.1051/0004-6361/201321457

ISSN: 0004-6361,1432-0746

Proyecto español: AYA2010-21490-C02-01

Url de la publicación: https://doi.org/10.1051/0004-6361/201321457