The FeII Optical Emission in AGN

We investigated the optical FeII emission in a sample of about 215 low-redshift AGN (quasars and luminous Seyfert 1 galaxies). We find that a scaled and broadened FeII template based on the I Zw 1 spectrum can satisfactorily model the FeII emission in almost all sources in our sample. We confirm that FWHM H$\beta$ and FeII$\lambda$4570 are strongly correlated. The correlation is different for sources with FWHM(H$\beta$) greater than or less than $\sim$4000 km s${}^{-1}$. Sources with FWHM H$\beta$$\le$ 4000 km s${}^{-1}$ (Population A) show no difference between FWHM H$\beta$ and FeII while sources with FWHM(H$\beta$) $\ge$ 4000 km s${}^{-1}$ (Population B) show FWHM FeII that is systematically smaller than FWHM H$\beta$. This may be telling us that FeII emission in Pop. B sources comes from only the outermost part of the H$\beta$
emitting region where the degree of ionization is lowest.