  We present a new catalog of narrow-line Seyfert 1 (NLSy1) galaxies from the
Sloan Digital Sky Survey Data Release 12 (SDSS DR12). This was obtained by a
systematic analysis through modeling of the continuum and emission lines of the
spectra of all the 68,859 SDSS DR12 objects that are classified as "QSO" by the
SDSS spectroscopic pipeline with z < 0.8 and a median signal-to-noise ratio
(S/N) > 2 per pixel. This catalog contains a total of 11,101 objects, which is
about 5 times larger than the previously known NLSy1 galaxies. Their
monochromatic continuum luminosity at 5100 A is found to be strongly correlated
with H-beta, H-alpha, and [O III] emission line luminosities. The optical Fe II
strength in NLSy1 galaxies is about two times larger than the broad- line
Seyfert 1 (BLSy1) galaxies. About 5% of the catalog sources are detected in the
FIRST survey. The Eddington ratio (XEdd) of NLSy1 galaxies has an average of
log XEdd of -0.34, much higher than -1.03 found for BLSy1 galaxies. Their black
hole masses (MBH) have an average of log MBH of 6.9 Msun, which is less than
BLSy1 galaxies, which have an average of log MBH of 8.0 Msun. The MBH of NLSy1
galaxies is found to be correlated with their host galaxy velocity dispersion.
Our analysis suggests that geometrical effects playing an important role in
defining NLSy1 galaxies and their MBH deficit is perhaps due to their lower
inclination compared to BLSy1 galaxies.
