On the size evolution of early type galaxies and their dark matter haloes

GRANATO, GIAN LUIGI; RAGONE FIGUEROA, CINTHIA; ABADI, MARIO GABRIEL

Trieste

Workshop; COSMOCOMP Workshop Trieste; 2012

INSTITUTE FOR COMPUTATIONAL COSMOLOGY, DURHAM UNIVERSITY

We perform controlled numerical experiments to asses the effect of baryon mass loss on the inner structure of large galactic dark matter (DM) haloes. This mass expulsion is intended to mimic both the supernova and active galactic nucleus (AGN) feedbacks, as well as the evolution of stellar populations. This study is meant in particular for precursors of massive early-type galaxies (ETGs), wherein strong AGN feedback (often dubbed ?quasi-stellar object mode? in galaxy formation models) has been proposed to remove on a short time-scale, 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. Here we focus on the distribution of DM 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 time-scale. 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.