Unveiling dark halos in lensing galaxies

TL;DR

This study compares the stellar and total mass distributions in nine early-type lensing galaxies, revealing dark matter's increasing dominance at larger radii and challenging certain stellar initial mass functions.

Contribution

It provides spatially resolved comparisons of stellar and total mass in lensing galaxies, highlighting dark matter distribution and IMF constraints.

Findings

Stars can account for all inner-region mass

Salpeter IMF overestimates stellar mass in inner regions

Dark matter dominates beyond the half-light radius

Abstract

We present a spatially resolved comparison of the stellar-mass and total-mass surface distributions of nine early-type galaxies. The galaxies are a subset of the Sloan Lens ACS survey (or SLACS; Bolton et al. 2006). The total-mass distributions are obtained by exploring pixelated mass models that reproduce the lensed images. The stellar-mass distributions are derived from population synthesis models fit to the photometry of the lensing galaxies. Uncertainties - mainly model degeneracies - are also computed. Stars can account for all the mass in the inner regions. A Salpeter IMF actually gives too much stellar mass in the inner regions and hence appears ruled out. Dark matter becomes significant by the half-light radius and becomes increasingly dominant at larger radii. The stellar and dark components are closely aligned, but the actual ellipticities are not correlated. Finally, we attempt to intuitively summarize the results by rendering the density, stellar-vs-dark ratio, and uncertainties as false-colour maps.