The CIV Baldwin effect in QSOs from Seventh Data Release of the Sloan Digital Sky Survey

TL;DR

This study confirms the presence of the Baldwin effect in a large sample of SDSS DR7 QSOs up to redshift 5, analyzing its slope evolution and underlying physical drivers, notably the Eddington ratio.

Contribution

It provides a comprehensive analysis of the Baldwin effect in over 35,000 QSOs, revealing its consistent existence across redshifts and identifying the Eddington ratio as a key physical parameter.

Findings

Baldwin effect exists up to z~5 in SDSS QSOs.

The slope of the effect varies with redshift, increasing from z~1.5 to 2.0.

Eddington ratio correlates more strongly with iv EW than black hole mass.

Abstract

Using the properties of SDSS DR7 QSOs catalog from Shen et al., the Baldwin effect, its slope evolution, the underlying drive for a large sample of 35019 QSOs with reliable spectral analysis are investigated. We find that the Baldwin effect exists in this large QSOs sample, which is almost the same in 11 different redshift bins, up to $z\sim 5$. The slope is -0.238 by the BCES (\civ\ EW depends on the continuum), -0.787 by the BCES bisector. For 11 redshift-bins, there is an increasing of the Baldwin effect slope from $z\sim1.5$ to $z\sim2.0$. From $z\sim2.0$ to $z\sim5.0$, the slope change is not clear considering their uncertainties or larger redshift bins. There is a strong correlation between the rest-frame \civ\ EW and \civ-based \mbh while the relation between the \civ\ EW and \mgii-based \mbh is very weak. With the correction of \civ-based \mbh from the \civ\ blueshift relative to \mgii, we suggest that this strong correlation is due to the bias of the \civ-based \mbh, with respect to that from the \mgii\ line. Considering the \mgii-based \mbh, a medium strong correlation is found between the \civ\ EW and the Eddington ratio, which implies that the Eddington ratio seems to be a better underlying physical parameter than the central black hole mass.