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Description
In this work, the authors present the most comprehensive INTEGRAL active galactic nucleus (AGN) sample. It lists 272 AGN for which they have secure optical identifications, precise optical spectroscopy and measured redshift values plus X-ray spectral information, i.e. 2-10 and 20-100 keV fluxes plus column densities. In their paper, the authors mainly use this sample to study the absorption properties of active galaxies, to probe new AGN classes and to test the AGN unification scheme. The authors find that half (48%) of the sample is absorbed, while the fraction of Compton-thick AGN is small (~7%). In line with their previous analysis, they have however shown that when the bias towards heavily absorbed objects which are lost if weak and at large distance is removed, as is possible in the local Universe, the above fractions increase to become 80% and 17%, respectively. The authors also find that absorption is a function of source luminosity, which implies some evolution in the obscuration properties of AGN. A few peculiar classes, so far poorly studied in the hard X-ray band, have been detected and studied for the first time such as 5 X-ray bright optically normal galaxies (XBONGs), 5 type 2 QSOs and 11 low-ionization nuclear emission regions. In terms of optical classification, this sample contains 57% type 1 and 43% type 2 AGN; this subdivision is similar to that found in X-rays if unabsorbed versus absorbed objects are considered, suggesting that the match between optical and X-ray classifications is on the whole good. Only a small percentage of sources (12%) does not fulfill the expectation of the unified theory as the authors find 22 type 1 AGN which are absorbed and 10 type 2 AGN which are unabsorbed. Studying in depth these outliers they found that most of the absorbed type 1 AGN have X-ray spectra characterized by either complex or warm/ionized absorption more likely due to ionized gas located in an accretion disc wind or in the bi-conical structure associated with the central nucleus, therefore unrelated to the toroidal structure. Among the 10 type 2 AGN which are unabsorbed, at most 3-4% are still eligible to be classified as 'true' type 2 AGN. In the fourth INTEGRAL/IBIS survey (Bird et al. 2010, ApJS, 186, 1, available in the HEASARC database as the IBISCAT4 table), there are 234 objects which have been identified with AGN. To this set of sources, the present authors then added 38 galaxies listed in the INTEGRAL all-sky survey by Krivonos et al. (2007, A&A, 475, 775, available in the HEASARC database as the INTIBISASS table) updated on the website (<a href="http://hea.iki.rssi.ru/integral/survey/catalog.php">http://hea.iki.rssi.ru/integral/survey/catalog.php</a>) but not included in the Bird et al. catalog due to the different sky coverage (these latter sources are indicated with hard_flag = 'h' values in this HEASARC table). The final data set presented and discussed in the reference paper and constituting this table therefore comprises 272 AGN and was last updated in March 2011 March. It represents the most complete view of the INTEGRAL extragalactic sky as of the date of publication in 2012. This table was created by the HEASARC in October 2014 based on CDS Catalog J/MNRAS/426/1750 files tablea1.dat and refs.dat. This is a service provided by NASA HEASARC .
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