The black hole mass - stellar velocity dispersion relation of
  narrow-line Seyfert 1 galaxies
  Narrow-line Seyfert 1 galaxies (NLS1s) are arguably one of the key AGN
subclasses in investigating the origin of the black hole mass - stellar
velocity dispersion (M-sigma) relation because of their high accretion rate and
significantly low black hole mass. Currently, it is under discussion whether
present-day NLS1s offset from the M-sigma relation. Using the directly measured
stellar velocity dispersion of 93 NLS1s at z<0.1, and black hole mass estimates
based on the updated mass estimators, we investigate the M-sigma relation of
NLS1s in comparison with broad-line AGNs. We find no strong evidence that the
NLS1s deviates from the M-sigma relation, which is defined by
reverberation-mapped type 1 AGNs and quiescent galaxies. However, there is a
clear trend of the offset with the host galaxy morphology, i.e., more inclined
galaxies toward the line-of-sight have higher stellar velocity dispersion,
suggesting that the rotational broadening plays a role in measuring stellar
velocity dispersion based on the single-aperture spectra from the Sloan Digital
Sky Survey. In addition, we provide the virial factor log f = $0.05 \pm 0.12$
(f = 1.12), for black hole mass estimators based on the FWHM of H$\beta$, by
jointly fitting the M-sigma relation using quiescent galaxies and
reverberation-mapped AGNs.
