Assessing the effect of lens mass model in cosmological application with updated galaxy-scale strong gravitational lensing sample

TL;DR

This study evaluates how different lens mass models affect cosmological parameter constraints using a large sample of galaxy-scale strong lensing systems, highlighting the importance of accounting for the density profile dependencies.

Contribution

It introduces a comprehensive analysis of the impact of lens mass model assumptions on cosmological constraints with the largest available lensing sample, emphasizing the need to consider redshift and surface density dependencies.

Findings

Weak and biased constraints on Ω_m when assuming a universal δ.

Unbiased Ω_m estimate (0.381^{+0.185}_{-0.154}) achieved when including γ dependence on redshift and surface density.

Significant dependence of results on the lens mass model and density profile parameters.

Abstract

By comparing the dynamical and lensing masses of early-type lens galaxies, one can constrain both the cosmological parameters and the density profiles of galaxies. We explore the constraining power on cosmological parameters and the effect of the lens mass model in this method with 161 galaxy-scale strong lensing systems, which is currently the largest sample with both high resolution imaging and stellar dynamical data. We assume a power-law mass model for the lenses, and consider three different parameterizations for $\gamma$ (i.e., the slope of the total mass density profile) to include the effect of the dependence of $\gamma$ on redshift and surface mass density. When treating $\delta$ (i.e., the slope of the luminosity density profile) as a universal parameter for all lens galaxies, we find the limits on the cosmological parameter $\Omega_m$ are quite weak and biased, and also heavily dependent on the lens mass model in the scenarios of parameterizing $\gamma$ with three different forms. When treating $\delta$ as an observable for each lens, the unbiased estimate of $\Omega_m$ can be obtained only in the scenario of including the dependence of $\gamma$ on both the redshift and the surface mass density, that is $\Omega_m = 0.381^{+0.185}_{-0.154}$ at 68\% confidence level in the framework of a flat $\Lambda$CDM model. We conclude that the significant dependencies of $\gamma$ on both the redshift and the surface mass density, as well as the intrinsic scatter of $\delta$ among the lenses, need to be properly taken into account in this method.