Low-Ionization Outflows in High Eddington Ratio Quasars

TL;DR

This study investigates broad MgII emission in high Eddington ratio quasars, revealing that in the most extreme cases, MgII shows blueshifts indicating outflows, which impacts its reliability for black hole mass estimation.

Contribution

It identifies the presence of outflows in high Eddington ratio quasars and shows that MgII line widths can be affected by these outflows, challenging their use for virial mass estimates.

Findings

MgII 2800 is narrower than Hbeta in most quasars

In high Eddington ratio quasars, MgII shows blueshift and broadening

Outflows affect ~10% of quasars, impacting mass estimation

Abstract

The broad MgII doublet has been much studied in connection with its potentially important role as a virial estimator of black hole mass in high redshift quasars. An important task is therefore identification of any line components likely related to broadening by non-virial motions. High s/n median composite spectra (binned in the "4D eigenvector 1" context of Sulentic et al. 2007) were constructed for the brightest 680 SDSS DR7 quasars in the 0.4 < z < 0.75 range where both MgII 2800 and Hbeta are recorded in the same spectra. Composite spectra representing 90% of the quasars confirm previous findings that FWHM(MgII 2800) is about 20% narrower than FWHM(Hbeta). The situation is clearly different for the most extreme (Population A) sources which are the highest Eddington radiators in the sample. In the median spectra of these sources FWHM MgII 2800 is equal to or greater than FWHM(Hbeta) and shows a significant blueshift relative to Hbeta. We interpret the MgII 2800 blueshift as the signature of a radiation-driven wind or outflow in the highest accreting quasars. In this interpretation the MgII 2800 line width -- affected by blueshifted emission -- is unsuitable for virial mass estimation in ~ 10% of quasars.