X-ray absorption in INTEGRAL AGN: Host galaxy inclination

Abstract

In this work the INTEGRAL hard X-ray selected sample of AGN has been used to investigate the possible contribution of absorbing material distributed within the host galaxies to the total amount of NH measured in the X-ray band. We collected all the available axial ratio measurements of the galaxies hosting our AGN together with their morphological information and find that also for our hard X-ray selected sample a deficit of edge-on galaxies hosting type 1 AGN is present. We estimate that in our hard X-ray selected sample there is a deficit of 24% (+/- 5%) of type 1 AGN. Possible bias in redshift has been excluded, as we found the same effect in a well determined range of z where the number and the distributions of the two classes are statistically the same. Our findings clearly indicate that material located in the host galaxy on scales of hundreds of parsecs and not aligned with the putative absorbing torus of the AGN can contribute to the total amount of column density. This galactic absorber can be large enough to hide the broad line region of some type 1 AGN causing their classification as type 2 objects and giving rise to the deficiency of type 1 in edge-on galaxies.