Systematic variation of central mass density slope in early-type galaxies

TL;DR

This study investigates how the total mass density slope varies in the central regions of early-type galaxies, revealing a non-universal profile that depends on galaxy mass and size, influenced by dissipative processes.

Contribution

It provides the first systematic analysis of the variation in density slopes in ETGs using detailed modeling and explores the impact of different dark matter profiles and galaxy properties.

Findings

Massive ETGs have near-isothermal density profiles.

Lower-mass ETGs exhibit steeper than isothermal profiles.

Density slope correlates with galaxy mass and size, indicating non-homology.

Abstract

We study the total density distribution in the central regions ($<\, 1$ effective radius, $R_{\rm e}$) of early-type galaxies (ETGs), using data from the SPIDER survey. We model each galaxy with two components (dark matter halo + stars), exploring different assumptions for the dark matter (DM) halo profile, and leaving stellar mass-to-light ($M_{\rm \star}/L$) ratios as free fitting parameters to the data. For a Navarro et al. (1996) profile, the slope of the total mass profile is non-universal. For the most massive and largest ETGs, the profile is isothermal in the central regions ($\sim R_{\rm e}/2$), while for the low-mass and smallest systems, the profile is steeper than isothermal, with slopes similar to those for a constant-M/L profile. For a concentration-mass relation steeper than that expected from simulations, the correlation of density slope with mass tends to flatten. Our results clearly point to a "non-homology" in the total mass distribution of ETGs, which simulations of galaxy formation suggest may be related to a varying role of dissipation with galaxy mass.