Bayesian analysis of joint strong gravitational lensing and dynamic galactic mass in SLACS: evidence of line-of-sight contamination

TL;DR

This study uses Bayesian analysis to compare galaxy mass estimates from strong gravitational lensing and stellar dynamics, revealing significant line-of-sight contamination that biases mass and density profile measurements.

Contribution

It introduces a Bayesian framework to jointly analyze lensing and dynamical data, accounting for line-of-sight contamination, and provides new insights into galaxy mass profiles.

Findings

Line-of-sight contamination significantly biases mass estimates.

The best-fit density profile follows a power-law with index -1.69.

Neglecting contamination overestimates galaxy mass from lensing.

Abstract

We readdress the calculation of the mass of early-type galaxies using strong gravitational lensing and stellar dynamics. Our sample comprises 27 galaxies in the Sloan Lens ACS (SLACS) Survey. Comparing the mass estimates from these two independent methods in a Bayesian framework, we find evidence of significant line-of-sight mass contamination. Assuming a power-law mass distribution, the best fit density profile is given by $\rho \propto r^{-1.69\pm0.05}$. We show that neglecting the line-of-sight mass contamination produces an overestimate of the mass attributed to the lens-galaxy by the lensing method, which introduces a bias in favor of a SIS profile when using the joint lensing and dynamic analysis to determine the slope of the density profile. We suggest that the line-of-sight contamination could also be important for other astrophysical and cosmological uses of joint lensing and dynamical measurements.