X-Ray And Optical Flux Ratio Anomalies In Quadruply Lensed Quasars. II. Mapping the Dark Matter Content in Elliptical Galaxies

TL;DR

This study uses X-ray microlensing data from multiple quasars to map the distribution of dark matter and stellar matter in elliptical galaxies, revealing a predominantly dark matter composition at certain radii.

Contribution

It provides the first detailed mapping of dark matter content in elliptical galaxies using microlensing analysis of X-ray flux ratios in quadruply lensed quasars.

Findings

Most likely local stellar fraction is 7%.

Dark matter constitutes about 93% of the mass.

Stellar fraction decreases with increasing impact parameter R_c.

Abstract

We present a microlensing analysis of 61 Chandra observations of 14 quadruply lensed quasars. X-ray flux measurements of the individual quasar images give a clean determination of the microlensing effects in the lensing galaxy and thus offer a direct assessment of the local fraction of stellar matter making up the total integrated mass along the lines of sight through the lensing galaxy. A Bayesian analysis of the ensemble of lensing galaxies gives a most likely local stellar fraction of 7%, with the other 93% in a smooth, dark matter component, at an average impact parameter R_c of 6.6 kpc from the center of the lensing galaxy. We divide the systems into smaller ensembles based on R_c and find that the most likely local stellar fraction varies qualitatively and quantitatively as expected, decreasing as a function of R_c.