The Role of Secular Evolution in the Black Hole Growth of Narrow-Line
  Seyfert 1 Galaxies
  Narrow-Line Seyfert 1 (NLS1) galaxies show extreme properties with respect to
the other Seyfert galaxies. Indeed, they are thought to be accreting at
Eddington rates and to possess low mass black holes. Therefore, they may
represent a key class of objects for understanding the co-evolution of black
holes and their host galaxies. We propose that NLS1s represent a class of AGN
in which the black hole growth is, and has always been, dominated by secular
evolution. Firstly, by looking at the NLS1 host galaxy properties in the
literature, we show that the evolution of NLS1s is presently driven by secular
processes, much more so than for Broad-Line Seyfert 1s (BLS1s). Secondly, we
study the bulges of NLS1 and BLS1 galaxies. Our results demonstrate that NLS1
host bulges are pseudo-bulges and are statistically different from BLS1 bulges.
This difference points to the particular importance of secular processes in the
past evolution of their hosts. We build on this result to understand the
implications on their evolution and the duration of their duty cycle. We show
that NLS1s are not necessarily in a special phase of black hole growth and that
several Gyr are required for their black hole masses to become similar to
BLS1s. Finally, in the light of our results, we discuss the location of NLS1
galaxies on the MBH-\sigma plane and speculate about the connection between the
NLS1 galaxy properties and their black hole spin.
