The SL2S Galaxy-scale Lens Sample. V. Dark Matter Halos and Stellar IMF of Massive Early-type Galaxies out to Redshift 0.8

TL;DR

This study analyzes the evolution of dark matter and stellar initial mass function in massive early-type galaxies up to redshift 0.8 using lensing and stellar dynamics, revealing trends in dark matter distribution and IMF normalization.

Contribution

It provides new insights into the cosmic evolution of dark matter halos and stellar IMF in massive galaxies through a joint lensing and dynamics analysis with Bayesian inference.

Findings

Dark matter within 5 kpc increases with redshift

IMF normalization is close to Salpeter and scales with stellar mass

No significant IMF dependence on redshift or stellar density

Abstract

We investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the Universe. We perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the SL2S and SLACS surveys and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar IMF across the population of massive early-type galaxies. Lensing selection effects are taken into account. We find that the dark matter mass projected within the inner 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of an NFW profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at $\log{M_*} = 11.5$ and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.