Effects of Baryon Mass Loss on Profiles of Large Galactic Dark Matter Haloes

TL;DR

This study uses numerical experiments to show that baryon mass loss from galactic dark matter haloes causes the inner regions to expand and flatten, challenging the compatibility of cuspy profiles with strong feedback processes.

Contribution

It demonstrates how baryon mass loss affects dark matter halo profiles, highlighting the limitations of simplified models and implications for galaxy evolution theories.

Findings

Inner halo regions expand and flatten after baryon loss

Approximate models underestimate halo expansion effects

Cuspy profiles are difficult to reconcile with strong feedback

Abstract

We perform controlled numerical experiments to asses the effect of baryon mass loss on the inner structure of large galactic dark matter haloes. This mass expulsion is intended to mimic both the supernovae and AGN feedbacks, as well as the evolution of stellar populations. This study is meant in particular for precursors of massive Early Type Galaxies, wherein strong AGN feedback (often dubbed "QSO mode" in galaxy formation models) has been proposed to remove on a short timescale, of the order of a few dynamical times, a substantial fraction of their baryons. In a previous paper we evaluated the observational consequences (size increase) of this process on the galactic structure (Ragone-Figueroa & Granato 2011). Here we focus on the distribution of dark matter in the galactic region. It is shown that the inner region of the DM halo expands and its density profile flattens by a sizeable amount, with little dependence on the expulsion timescale. We also evaluate the effect of the commonly made approximation of treating the baryonic component as a potential that changes in intensity without any variation in shape. This approximation leads to some underestimates of the halo expansion and its slope flattening. We conclude that cuspy density profiles in ETGs could be difficult to reconcile with an effective AGN (or stellar) feedback during the evolution of these systems.