Microlensing of Quasar Broad Emission Lines: Constraints on Broad Line Region Size

Abstract

We measure the differential microlensing of the broad emission lines between 18 quasar image pairs in 16 gravitational lenses. We find that the broad emission lines are in general weakly microlensed. The results show, at a modest level of confidence (1.8σ), that high ionization lines such as CIV are more strongly microlensed than low ionization lines such as Hβ, indicating that the high ionization line emission regions are more compact. If we statistically model the distribution of microlensing magnifications, we obtain estimates for the broad line region size of r s = 24 +22 −15 and r s = 55 +150 −35 light-days (90% confidence) for the high and low ionization lines, respectively. When the samples are divided into higher and lower luminosity quasars, we find that the line emission regions of more luminous quasars are larger, with a slope consistent with the expected scaling from photoionization models. Our estimates also agree well with the results from local reveberation mapping studies.

The different origins of high- and low-ionization broad emission lines revealed by gravitational microlensing in the Einstein cross

“…By contrast, the polar wind model is the only one that leads to comparable magnification of the very blueshifted and redshifted parts of the line profile when seen at intermediate inclination, whatever the magnifying caustic structure. Among the 18 quasars for which microlensing of the high-ionization lines is observed (Richards et al 2004;Sluse et al 2012;Guerras et al 2013), only SDSS J1004+4112 shows a significant differential magnification of the blue and red wings in the CIV line profile; if indeed caused by microlensing, this could constitute an important blow to high-ionized gas flowing as a wind. Further study of this object is badly needed.…”

Dark Matter Mass Fraction in Lens Galaxies: New Estimates From Microlensing

“…Only the system RXS J1131−1231 is excluded, as it was observed in [O iii] at a much larger wavelength of ∼5000 Å. These microlensing magnification estimates are calculated after subtracting the emission line flux ratios, which are little affected by microlensing (see, e.g., Guerras et al 2013), from the continuum flux ratios, and are therefore virtually free from extinction, substructure, and macro model effects (as these affect the line and continuum flux ratios equally). Our strategy is to compare the observed microlensing magnification for a given image pair Δm obs i with a statistical sample of simulated values for that measurement as a function of the source size (r s ) and the fraction of surface mass density in stars (α).…”

“…The problem is that the anomalies are usually identified assuming that a standard macrolens model can be used as an absolute "flux ratio" reference without contamination by differential extinction (e.g., Falco et al 1999;Muñoz et al 2004) or perturbations from substructures in the lens (e.g., Dalal & Kochanek 2002;Keeton et al 2003). One solution is to use emission line ratios, which are little affected by microlensing (e.g., Guerras et al 2013), as a baseline to remove the effects of the macro-magnification, extinction, and substructure (Mediavilla et al 2009, hereafter MED09). The problem remains of intrinsic source variability modulated by the lens time delays as a contribution of apparent flux anomalies.…”

Imprints of the quasar structure in time-delay light curves: Microlensing-aided reverberation mapping

“…The signal produced by microlensing on quasar light curves, is conceptually very similar to photometric reverberation mapping, but is potentially applicable to single band data. In addition, since microlensing provides an independent probe of the accretion disc and BLR size (Kochanek 2004;Eigenbrod et al 2008;Morgan et al 2010;Blackburne et al 2011;Sluse et al 2011;Guerras et al 2013), it offers a potentially more complete picture of the same sample of objects.…”

“…The microlensing effect can be used to probe the source at high resolution because it selectively magnifies its emission as a function of the size of the emitting region, provided the latter is smaller than ∼ 10 η 0 (Refsdal & Stabell 1997). Nowadays, quasar microlensing is employed to measure the size and temperature profile of the accretion disc, or the size and geometry of the broad line emitting region (Kochanek 2004;Sluse et al 2007;Eigenbrod et al 2008;Morgan et al 2010;Blackburne et al 2011;Sluse et al 2011;O'Dowd et al 2011;Guerras et al 2013).…”