On the average density profile of dark-matter halos in the inner regions of massive early-type galaxies

TL;DR

This study analyzes the inner dark-matter density profiles of massive early-type galaxies using strong lensing data, revealing profiles close to isothermal and highlighting baryonic effects on dark matter contraction.

Contribution

It provides the first combined analysis of dark matter profiles in early-type galaxies considering different stellar initial mass functions, linking baryonic effects to dark matter halo contraction.

Findings

Dark matter density profile slopes are near -1, consistent with isothermal profiles.

Results depend on the assumed stellar initial mass function.

Evidence supports baryonic influence on dark matter halo contraction.

Abstract

We study a sample of 39 massive early-type lens galaxies at redshift z < 0.3 to determine the slope of the average dark-matter density profile in the innermost regions. We keep the strong lensing and stellar population synthesis modeling as simple as possible to measure the galaxy total and luminous masses. By rescaling the values of the Einstein radius and dark-matter projected mass with the values of the luminous effective radius and mass, we combine all the data of the galaxies in the sample. We find that between 0.3 and 0.9 times the value of the effective radius the average logarithmic slope of the dark-matter projected density profile is -1.0 +/- 0.2 (i.e., approximately isothermal) or -0.7 +/- 0.5 (i.e., shallower than isothermal), if, respectively, a constant Chabrier or heavier, Salpeter-like stellar IMF is adopted. These results provide positive evidence of the influence of the baryonic component on the contraction of the galaxy dark-matter halos, compared to the predictions of dark matter-only cosmological simulations, and open a new way to test models of structure formation and evolution within the standard LCDM cosmological scenario.