The nature and origin of Narrow Line AGN activity in a sample of
  isolated SDSS galaxies
  We discuss the nature and origin of the nuclear activity observed in a sample
of 292 SDSS narrow-emission-line galaxies, considered to have formed and
evolved in isolation. All these galaxies are spiral like and show some kind of
nuclear activity. The fraction of Narrow Line AGNs (NLAGNs) and Transition type
Objects (TOs; a NLAGN with circumnuclear star formation) is relatively high,
amounting to 64% of the galaxies. There is a definite trend for the NLAGNs to
appear in early-type spirals, while the star forming galaxies and TOs are found
in later-type spirals. We verify that the probability for a galaxy to show an
AGN characteristic increases with the bulge mass of the galaxy (Torre-Papaqui
et al. 2011), and find evidence that this trend is really a by-product of the
morphology, suggesting that the AGN phenomenon is intimately connected with the
formation process of the galaxies. Consistent with this interpretation, we
establish a strong connection between the astration rate--the efficiency with
which the gas is transformed into stars--the AGN phenomenon, and the
gravitational binding energy of the galaxies: the higher the binding energy,
the higher the astration rate and the higher the probability to find an AGN.
The NLAGNs in our sample are consistent with scaled-down or powered-down
versions of quasars and Broad Line AGNs.
