A Systematic Analysis of Fe II Emission in Quasars: Evidence for Inflow to the Central Black Hole

• Published in: The Astrophysical journal 2008-11, Vol.687 (1), p.78-96
• Main Authors: Hu, Chen, Wang, Jian-Min, Ho, Luis C, Chen, Yan-Mei, Zhang, Hao-Tong, Bian, Wei-Hao, Xue, Sui-Jian
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/591838

Broad Fe ii emission is a prominent feature of the optical and ultraviolet spectra of quasars. We report on a systematical investigation of optical Fe ii emission in a large sample of 4037 [image] quasars selected from the Sloan Digital Sky Survey. We have developed and tested a detailed line-fitting technique, taking into account the complex continuum and narrow and broad emission-line spectra. Our primary goal is to quantify the velocity broadening and velocity shift of the Fe ii spectrum in order to constrain the location of the Fe II-emitting region and its relation to the broad-line region. We find that the majority of quasars show Fe ii emission that is redshifted, typically by [image]400 km s super(-1), but up to 2000 km s super(-1), with respect to the systemic velocity of the narrow-line region or of the conventional broad-line region as traced by the H beta line. Moreover, the line width of Fe ii is significantly narrower than that of the broad component of H beta . We show that the magnitude of the Fe ii redshift correlates inversely with the Eddington ratio, and that there is a tendency for sources with redshifted Fe ii emission to show red asymmetry in the H beta line. These characteristics strongly suggest that Fe ii originates from a location different from, and most likely exterior to, the region that produces most of H beta . The Fe ii-emitting zone traces a portion of the broad-line region of intermediate velocities whose dynamics may be dominated by infall.