Narrow-line Seyfert 1 galaxies: an amasing class of AGN
  [Abridged] Narrow-line Seyfert 1 (NLS1) galaxies are a class of active
galactic nuclei (AGN) that have all the properties of type 1 Seyfert galaxies
but show peculiar characteristics, including the narrowest Balmer lines,
strongest Fe II emission, and extreme properties in the X-rays. Line and
continuum radio observations provide an optimal tool to access the (often)
optically obscured innermost regions of AGN and reveal the kinematics of the
gas around their central engines. We investigate the interplay between the
peculiar NLS1 class of AGN and the maser phenomenon, to help us understand the
nature of the maser emission in some NLS1s where water maser emission has been
detected. We observed a sample of NLS1 galaxies with the Green Bank Telescope
in a search for water maser emission at 22 GHz. We also reduced and analysed
archival Green Bank Telescope and Very Large Array data and produced 22-GHz
spectra for the five NLS1 galaxies with detected maser emission. In particular,
we imaged the maser and nuclear radio continuum of NGC5506 at subarcsec scales
with the Very Large Array. We discovered maser emission in two NLS1 galaxies:
IGRJ16385-2057, and IRAS03450+0055. In addition to the three previously known
maser detections in the NLS1s Mrk766, NGC4051, and NGC5506, this yields a water
maser detection rate in NLS1 galaxies of ~7% (5/71). This value rises
significantly to ~21% (5/24) when considering only NLS1 galaxies at recessional
velocities less than 10000 km/s. For NGC4051 and NGC5506, we find that the
water maser emission is located within 5 and 12 pc, respectively, of nuclear
radio continuum knots, which are interpreted as core-jet structures.
