Περίληψη:
Aims. The main purpose of this study is to investigate aspects regarding
the validity of the active galactic nucleus (AGN) unification paradigm
(UP). In particular, we focus on the AGN host galaxies, which according
to the UP should show no systematic differences depending on the AGN
classification.
Methods. For the purpose of this study, we used (a) the spectroscopic
Sloan Digital Sky Survey (SDSS) Data Release 14 catalogue, in order to
select and classify AGNs using emission line diagnostics, up to a
redshift of z=0.2, and (b) the Galaxy Zoo Project catalogue, which
classifies SDSS galaxies in two broad Hubble types: spirals and
ellipticals.
Results. We find that the fraction of type 1 Seyfert nuclei (Sy1) hosted
in elliptical galaxies is significantly larger than the corresponding
fraction of any other AGN type, while there is a gradient of increasing
spiral-hosts from Sy1 to LINER, type 2 Seyferts (Sy2) and composite
nuclei. These findings cannot be interpreted within the simple unified
model, but possibly by a co-evolution scheme for supermassive black
holes and galactic bulges. Furthermore, for the case of spiral host
galaxies we find the Sy1 population to be strongly skewed towards
face-on configurations, while the corresponding Sy2 population range in
all host galaxy orientation configurations has a similar, but not
identical, orientation distribution to star-forming galaxies. These
results also cannot be interpreted by the standard unification paradigm,
but point towards a significant contribution of the galactic disc to the
obscuration of the nuclear region. This is also consistent with the
observed preference of Sy1 nuclei to be hosted by ellipticals, that is,
the dusty disc of spiral hosts contributes to the obscuration of the
broad-line region, and thus relatively more ellipticals are expected to
appear hosting Sy1 nuclei.
Συγγραφείς:
Gkini, Anamaria
Plionis, Manolis
Chira, Maria
Koulouridis,
Elias
