The Co-Evolution of Total Density Profiles and Central Dark Matter Fractions in Simulated Early-Type Galaxies

TL;DR

This paper uses cosmological simulations to explore how the total density profile slope and dark matter fraction in early-type galaxies co-evolve, revealing a relation influenced by feedback processes and redshift, with implications for galaxy formation models.

Contribution

It demonstrates a co-evolution relation between density slope and dark matter fraction across redshifts and feedback models, providing a new test for galaxy formation theories.

Findings

Density slope and dark matter fraction are correlated across redshifts.

Feedback models affect the relation's parameters, offering a way to test these models.

Simulations predict steeper density slopes at higher redshifts, conflicting with lensing observations unless observational biases are considered.

Abstract

We present evidence from cosmological hydrodynamical simulations for a co-evolution of the slope of the total (dark and stellar) mass density profile, gamma_tot, and the dark matter fraction within the half-mass radius, f_DM, in early-type galaxies. The relation can be described as gamma_tot = A f_DM + B for all systems at all redshifts. The trend is set by the decreasing importance of gas dissipation towards lower redshifts and for more massive systems. Early-type galaxies are smaller, more concentrated, have lower f_DM and steeper gamma_tot at high redshifts and at lower masses for a given redshift; f_DM and gamma_tot are good indicators for growth by "dry" merging. The values for A and B change distinctively for different feedback models, and this relation can be used as a test for such models. A similar correlation exists between gamma_tot and the stellar mass surface density Sigma_*. A model with weak stellar feedback and feedback from black holes is in best agreement with observations. All simulations, independent of the assumed feedback model, predict steeper gamma_tot and lower f_DM at higher redshifts. While the latter is in agreement with the observed trends, the former is in conflict with lensing observations, which indicate constant or decreasing gamma_tot. This discrepancy is shown to be artificial: the observed trends can be reproduced from the simulations using observational methodology to calculate the total density slopes.