NDLI: Reliable identification of compton-thick quasars at z ≈ 2: spitzer mid-infrared spectroscopy of hdf-omd49 (2008).

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Reliable identification of compton-thick quasars at z ≈ 2: spitzer mid-infrared spectroscopy of hdf-omd49 (2008).

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Abstract	Many models that seek to explain the origin of the unresolved X-ray background predict that Compton-thick Active Galactic Nuclei (AGNs) are ubiquitious at high redshift. However, few distant Compton-thick AGNs have been reliably identified to date. Here we present Spitzer-IRS spectroscopy and 3.6–70 µm photometry of a z = 2.211 optically identified AGN (HDF-oMD49) that is formally undetected in the 2 Ms Chandra Deep Field-North (CDF-N) survey. The Spitzer-IRS spectrum and spectral energy distribution of this object is AGN dominated, and a comparison of the energetics at X-ray wavelengths to those derived from mid-infrared (mid-IR) and optical spectroscopy shows that the AGN is intrinsically luminous (L2−10 keV ≈ 3 × 10 44 erg s −1) but heavily absorbed by Compton-thick material (NH ≫ 10 24 cm −2); i.e., this object is a Compton-thick quasar. Adopting the same approach that we applied to HDF-oMD49, we found a further six objects at z ≈ 2–2.5 in the literature that are also X-ray weak/undetected but have evidence for AGN activity from optical and/or mid-IR spectroscopy, and show that all of these sources are likely to be Compton-thick quasars with L2−10keV> 10 44 erg s −1. On the basis of the definition of Daddi et al. (2007), these Compton-thick quasars would be
File Format	PDF
Publisher Date	2008-01-01
Access Restriction	Open
Subject Keyword	Compton-thick Quasar Reliable Identification Spitzer Mid-infrared Spectroscopy X-ray Wavelength Many Model Agn Activity Distant Compton-thick Agns Mid-ir Spectroscopy Compton-thick Material Spectral Energy Distribution Optical Spectroscopy Show Present Spitzer-irs Spectroscopy Unresolved X-ray Background Predict High Redshift M Chandra Deep Field-north Spitzer-irs Spectrum Compton-thick Active Galactic Nucleus
Content Type	Text

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