On the dichotomy of Seyfert 2 galaxies: intrinsic differences and
  evolution
  We present a study of the local environment (<200 kpc/h) of 31 Hidden Broad
Line Region (HBLR) and 43 non-HBLR Seyfert 2 galaxies (Sy2) in the nearby
universe (z<0.04). To compare our findings, we constructed two control samples
that match the redshift and the morphological type distribution of the HBLR and
non-HBLR samples respectively. We used the NED (NASA extragalactic database) to
find all neighboring galaxies within projected radius of 200 kpc/h around each
galaxy, and radial velocity difference delta_u< 500 km/s. We find that, within
a projected radius of at least 150 kpc/h around each Seyfert, the fraction of
non-HBLR Sy2 galaxies with a close companion is significantly higher than that
of their control sample, at the 96% confidence level. Interestingly, the
difference is due to the high frequency of mergers in the non-HBLR sample,
seven versus only one in the control sample, while also they present a high
number of hosts with signs of peculiar morphology. In sharp contrast, the HBLR
sample is consistent with its control sample and furthermore, the number of
their host galaxies that present peculiar morphology, which probably implies
some level of interactions or merging in the past, is the lowest in all four
galaxy samples. Given that the HBLR Seyfert 2 galaxies are essentially Seyfert
1 (Sy1), with their broad line region (BLR) hidden because of the obscuration
by the torus, while the non-HBLR Sy2 sample probably also includes
intrinsically different objects, like "true" Sy2s that lack the BLR, and
heavily obscured objects that prohibit even its indirect detection, our results
are discussed within the context of an evolutionary sequence of activity
triggered by close galaxy interactions and merging. We argue that the non-HBLR
Sy2 galaxies may represent different stages of this sequence, possibly the
beginning and the end of the nuclear activity.
