  We present a statistical study of a large, homogeneously analyzed sample of
narrow-line Seyfert 1 (NLS1) galaxies, accompanied by a comparison sample of
broad-line Seyfert 1 (BLS1) galaxies. Optical emission-line and continuum
properties are subjected to correlation analyses, in order to identify the main
drivers of active galactic nuclei (AGN) correlation space, and of NLS1 galaxies
in particular. For the first time, we have established the density of the
narrow-line region as a key parameter in Eigenvector 1 space, as important as
the Eddington ratio L/Ledd. This is important because it links the properties
of the central engine with the properties of the host galaxy; i.e., the
interstellar medium (ISM). We also confirm previously found correlations
involving the line width of Hbeta, and the strength of the FeII and [OIII]5007
emission lines, and we confirm the important role played by L/Ledd in driving
the properties of NLS1 galaxies. A spatial correlation analysis shows that
large-scale environments of the BLS1 and NLS1 galaxies of our sample are
similar. If mergers are rare in our sample, accretion-driven winds on the one
hand, or bar-driven inflows on the other hand, may account for the strong
dependence of Eigenvector 1 on ISM density.

Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies