Analysis of optical Fe II emission in a sample of AGN spectra
  We present a study of optical Fe II emission in 302 AGNs selected from the
SDSS. We group the strongest Fe II multiplets into three groups according to
the lower term of the transition (b $^4$F, a $^6$S and a $^4$G terms). These
correspond approximately to the blue, central, and red part respectively of the
"iron shelf" around Hb. We calculate an Fe II template which takes into account
transitions into these three terms and an additional group of lines, based on a
reconstruction of the spectrum of I Zw 1. This Fe II template gives a more
precise fit of the Fe II lines in broad-line AGNs than other templates. We
extract Fe II, Ha, Hb, [O III] and [N II] emission parameters and investigate
correlations between them. We find that Fe II lines probably originate in an
Intermediate Line Region. We notice that the blue, red, and central parts of
the iron shelf have different relative intensities in different objects. Their
ratios depend on continuum luminosity, FWHM Hb, the velocity shift of Fe II,
and the Ha/Hb flux ratio. We examine the dependence of the well-known
anti-correlation between the equivalent widths of Fe II and [O III] on
continuum luminosity. We find that there is a Baldwin effect for [O III] but an
inverse Baldwin effect for the Fe II emission. The [O III]/Fe II ratio thus
decreases with L\lambda5100. Since the ratio is a major component of the
Boroson and Green eigenvector 1, this implies a connection between the Baldwin
effect and eigenvector 1, and could be connected with AGN evolution. We find
that spectra are different for Hb FWHMs greater and less than ~3000 km/s, and
that there are different correlation coefficients between the parameters.
