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

Abstract

We present a joint estimate of the stellar/dark matter mass fraction in lens galaxies and the average size of the accretion disk of lensed quasars based on microlensing measurements of 27 quasar image pairs seen through 19 lens galaxies. The Bayesian estimate for the fraction of the surface mass density in the form of stars is α = 0.21 ± 0.14 near the Einstein radius of the lenses (∼1-2 effective radii). The estimate for the average accretion disk size is R 1/2 = 7.9 +3.8 −2.6 √ M/0.3 M light days. The fraction of mass in stars at these radii is significantly larger than previous estimates from microlensing studies assuming quasars were point-like. The corresponding local dark matter fraction of 79% is in good agreement with other estimates based on strong lensing or kinematics. The size of the accretion disk inferred in the present study is slightly larger than previous estimates.

Limits on the Mass and Abundance of Primordial Black Holes from Quasar Gravitational Microlensing

“…The second result, already discussed in the stellar mass range (see Mediavilla et al 2009, Schechter et al 2014, Jiménez-Vicente et al 2015a, is that the estimated abundance of microlenses, α = 0.2 ± 0.05 (see Figures 1 and 2), is in good agreement with the expected abundance of stars in the lens galaxies (Jiménez-Vicente et al 2015a,b), leaving barely any room for an extra population of compact objects. We can wonder to what extent is this result dependent on the assumption that the microlenses mass distribution is degenerate with the single-mass case.…”

“…Our study is based on the data and simulations from Jiménez-Vicente et al (2015a) in the optical range, and Jiménez-Vicente et al (2015b) in X-rays, who used microlensing magnification measurements from 24 gravitationally lensed quasars. In these studies an estimate of the abundance of microlenses (i.e.…”

“…The resulting PDFs, L(M, α|∆m ij ), are shown in Figure 1 for the optical microlensing measurements analyzed in Jiménez-Vicente et al (2015a) corresponding to a rest wavelength of ∼1736Å and in Figure 2 for the X-ray data discussed in Jiménez-Vicente et al (2015b). The first result (see Figure 1) is that the optical data strongly constrain the compact object masses to the range 0.05M (r toward larger values could push up the limits 3 The fit of the combined RM and microlensing data by Edelson et al (2015) for M BH ∼ 10 9 M , gives r s = 6.5 lt-day.…”

Probing the Dark Matter Radial Profile in Lens Galaxies and the Size of X-Ray Emitting Region in Quasars With Microlensing

“…However, since microlensing is sensitive to both physical effects, some degeneracy was expected in the microlensing based estimates of these parameters (see MED09). This has been shown by Jiménez-Vicente et al (2015) who, despite the strong covariance between stellar mass fraction α and source size R 1 2 , found reasonably good estimates for both parameters of 0.21 0.14 α = ± at a radius of approximately R 1.8 e where R e is the effective radius of the lens, and Å, where M is the mean mass of the microlenses. Microlensing of multiply imaged quasars has also been observed in X-rays (e.g., Blackburne et al 2006Blackburne et al , 2014Blackburne et al , 2015Pooley et al 2006Pooley et al , 2007Morgan et al 2008Morgan et al , 2012Chartas et al 2009;Dai et al 2009Dai et al , 2010Mosquera et al 2013;MacLeod & Morgan 2013).…”

First Lensed Quasar Systems from the VST-ATLAS Survey: One Quad, Two Doubles, and Two Pairs of Lensless Twins*

“…Treu & Marshall (2016) present a current survey of the use of time-delay measurements for cosmography. The microlensing of lensed quasars can be used to determine sizes for the emitting regions of quasars (Rauch & Blandford 1991;Agol & Krolik 1999;Pooley et al 2007;Blackburne et al 2011) and to measure the dark matter fraction in lensing galaxies (Schechter & Wambsganss 2004;Pooley et al 2012;Jiménez-Vicente et al 2015). For each of these efforts the accuracy achieved is limited by the relatively small number of lensed systems.…”