Limits on the power-law mass and luminosity density profiles of elliptical galaxies from gravitational lensing systems

TL;DR

This study uses gravitational lensing data to analyze the mass and light distribution in elliptical galaxies up to redshift 1, revealing that dark matter extends differently than luminous matter and the density profile evolves over cosmic time.

Contribution

It provides new constraints on the power-law indices of mass and luminosity density profiles in elliptical galaxies, incorporating redshift evolution and mass dependence.

Findings

Total density profile slightly steepens over time.

Mass traces light is rejected with >95% confidence.

Intermediate-mass galaxies align with the singular isothermal sphere model.

Abstract

We use 118 strong gravitational lenses observed by the SLACS, BELLS, LSD and SL2S surveys to constrain the total mass profile and the profile of luminosity density of stars (light-tracers) in elliptical galaxies up to redshift $z \sim 1$. Assuming power-law density profiles for the total mass density, $\rho=\rho_0(r/r_0)^{-\alpha}$, and luminosity density, $\nu=\nu_0(r/r_0)^{-\delta}$, we investigate the power law index and its first derivative with respect to the redshift. Using Monte Carlo simulations of the posterior likelihood taking the Planck's best-fitted cosmology as a prior, we find $\gamma= 2.132\pm0.055$ with a mild trend $\partial \gamma/\partial z_l= -0.067\pm0.119$ when $\alpha=\delta=\gamma$, suggesting that the total density profile of massive galaxies could have become slightly steeper over cosmic time. Furthermore, similar analyses performed on sub-samples defined by different lens redshifts and velocity dispersions, indicate the need of treating low, intermediate and high-mass galaxies separately. Allowing $\delta$ to be a free parameter, we obtain $\alpha=2.070\pm0.031$, $\partial \alpha/\partial z_l= -0.121\pm0.078$, and $\delta= 2.710\pm0.143$. The model in which mass traces light is rejected at $>95\%$ confidence and our analysis robustly indicates the presence of dark matter in the form of a mass component that is differently spatially extended than the light. In this case, intermediate-mass elliptical galaxies ($200$ km/s $ < \sigma_{ap} \leq 300$ km/s) show the best consistency with the singular isothermal sphere as an effective model of galactic lenses.