Dust-to-gas ratio in a complete sample of type-1 AGN

Abstract

According to the Unified Model of Active Galactic Nuclei (AGN), unobscured AGN based on its optical spectrum (detection of rest-frame UV-optical broad emission lines, type-1 AGN) should appear as X-ray unabsorbed AGN. However, there is an important fraction (10-30%) of AGN whose optical and X-ray classifications do not match, and the origin of the discrepancy is not clear. To provide insight into this topic, we have conducted a statistical analysis of the optical obscuration and X-ray absorption properties of the optically type1 AGN from the Bright Ultra-hard XMM-Newton Survey (BUXS) with L2−10keV >1042 erg s−1 and z=0.05-1. We have high-quality spectra from XMM-Newton and either SDSS spectra or proprietary observations for the selected sample. In order to provide the most complete sample as possible, we have conducted a detailed analysis of the emission lines to provide a reliable classification of the AGNs. We derive the X-ray absorption by fitting their XMM-Newton spectra and the optical extinction using UV/optical spectral continuum fits. As BUXS is a flux limited X-ray selected sample at hard energies (f4.510keV ≤6×10−14 ergs−1cm−2), it is complete for NH column densities up to the Compton-thick limit (∼1024cm−2). Our preliminary results show that most type-1 AGN in our sample show consistent optical and X-ray classification, but there is a large fraction ( 20%) of objects with large NH column densities (NH >4×1021 cm−2).