Fe II and Mg II in Luminous, Intermediate-Redshift Narrow-line Seyfert 1 Galaxies from the Sloan Digital Sky Survey

Abstract

We present results from analysis of spectra from a sample of ~900 quasars from the Sloan Digital Sky Survey. These objects were selected for their intermediate redshift (1.2<z<1.8), placing MgII and UV FeII in the optical band pass, relatively narrow MgII lines, and moderately good signal-to-noise-ratio spectra. Using a maximum likelihood analysis, we discovered that there is a significant dispersion in the FeII/MgII ratios in the sample. Using simulations, we demonstrate that this range, and corresponding correlation between FeII equivalent width and FeII/MgII ratio, are primarily a consequence of a larger dispersion of FeII equivalent width (EW) relative to MgII EW. This larger dispersion in FeII EW could be a consequence of a range in iron abundance, or in a range of FeII excitation. The latter possibility is supported by evidence that objects with weak (zero) CII]λ2325 equivalent width are likely to have large FeII/MgII ratios. We discuss physical effects that could produce a range of FeII/MgII ratio.

Accepted for publication in ApJ. Spectral fitting and analysis substantially revised