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Aims.The main purpose of this study is to investigate aspects regarding thevalidity of the active galactic nucleus (AGN) unification paradigm (UP). Inparticular, we focus on the AGN host galaxies, which according to the UP shouldshow no systematic differences depending on the AGN classification. Methods.Forthe purpose of this study, we used (a) the spectroscopic Sloan Digital SkySurvey (SDSS) Data Release (DR) 14 catalogue, in order to select and classifyAGNs using emission line diagnostics, up to a redshift of z=0.2, and (b) theGalaxy Zoo Project catalogue, which classifies SDSS galaxies in two broadHubble types: spirals and ellipticals. Results.We find that the fraction oftype 1 Seyfert nuclei (Sy1) hosted in elliptical galaxies is significantlylarger than the corresponding fraction of any other AGN type, while there is agradient of increasing spiral-hosts from Sy1 to LINER, type 2 Seyferts (Sy2)and composite nuclei. These findings cannot be interpreted within the simpleunified model, but possibly by a co-evolution scheme for supermassive blackholes (SMBH) and galactic bulges. Furthermore, for the case of spiral hostgalaxies we find the Sy1 population to be strongly skewed towards face-onconfigurations, while the corresponding Sy2 population range in all host galaxyorientation configurations has a similar, but not identical, orientationdistribution to star-forming (SF) galaxies. These results also cannot beinterpreted by the standard unification paradigm, but point towards asignificant contribution of the galactic disc to the obscuration of the nuclearregion. This is also consistent with the observed preference of Sy1 nuclei tobe hosted by ellipticals, that is, the dusty disc of spiral hosts contributesto the obscuration of the broad-line region (BLR), and thus relatively moreellipticals are expected to appear hosting Sy1 nuclei.

Host galaxy and orientation differences between AGN different types