Emission Line Properties of Seyfert Galaxies in the 12 Micron Sample
  We present spectroscopy of emission lines for 81 Seyfert 1 and 104 Seyfert 2
galaxies in the IRAS 12$\mu$m galaxy sample. We analyzed the emission-line
luminosity functions, reddening, and other gas diagnostics. The narrow-line
regions (NLR) of Sy1 and 2 galaxies do not significantly differ from each other
in most of these diagnostics. Combining the H$\alpha$/H$\beta$ ratio with a new
reddening indicator-the [SII]6720/[OII]3727 ratio, we find the average
$E(B-V)=0.49\pm0.35$ for Sy1s and $0.52\pm0.26$ for Sy2s. The NLR of Sy1
galaxies has only marginally higher ionization than the Sy2s. Our sample
includes 22 Sy1.9s and 1.8s. In their narrow lines, these low-luminosity
Seyferts are more similar to the Sy2s than the Sy1s. We construct a BPT
diagram, and include the Sy1.8s and 1.9s. They overlap the region occupied by
the Sy2s. The C IV equivalent width correlates more strongly with [O
III]/H$\beta$ than with UV luminosity. The Sy1 and Sy2 luminosity functions of
[OII]3727 and [OIII]5007 are indistinguishable. Unlike the LF's of Seyfert
galaxies measured by SDSS, ours are nearly flat at low L. The larger number of
faint Sloan "AGN" is attributable to their inclusion of weakly emitting LINERs
and H II+AGN "composite" nuclei, which do not meet our classification criteria
for Seyferts. An Appendix investigates which emission line luminosities provide
the most reliable measures of the total non-stellar luminosity. The hard X-ray
or near-ultraviolet continuum luminosity can be crudely predicted from either
the [O III]5007 luminosity, or the combination of [O III]+H$\beta$, or [N
II]+H$\alpha$ lines, with a scatter of $\pm\,4$ times for the Sy1s and
$\pm\,10$ times for the Sy2s. The latter two hybrid (NLR+BLR) indicators have
the advantage of predicting the same HX luminosity independent of Seyfert type.
