A multifrequency characterization of the extragalactic hard X-ray sky

Abstract

Nowadays we know that the origin of the Cosmic X-ray Background (CXB) is due to the integrated emission of nearby active galactic nuclei. Thus, to obtain a precise estimate of the contribution of different source classes to the CXB it is crucial to fully characterize the hard X-ray sky. We present a multifrequency analysis of all sources listed in the 3d release of the Palermo Swift-BAT hard X-ray catalog (3PBC) with the goal of (i) identifying and classifying the largest number of sources adopting multifrequency criteria, with particular emphasis on extragalactic populations and (ii) extracting Seyfert galaxies to present here the 2nd release of the Turin-SyCAT catalog. We outline a classification scheme based on radio, infrared and optical criteria that allows us to distinguish between unidentified and unclassified hard X-ray sources, and classify and classify the remaining ones discriminating between Galactic and extragalactic classes. Our revised version of the 3PBC lists 1176 classified, 820 extragalactic, and 356 Galactic, 199 unclassified, and 218 unidentified sources. According to our analysis, the hard X-ray sky is mainly populated by Seyfert galaxies and blazars. For the Seyfert galaxies, we present the 2nd release of the Turin-SyCAT including a total of 633 Seyfert galaxies, with 282 new sources, which is an 80% increment from the previous release. We confirm, that there is no clear difference between the flux distribution of the infrared-to-hard X-ray flux ratio of Seyfert galaxies Type 1 and Type 2. However, we confirm a significant trend between the mid-IR flux and hard X-ray flux.