http://arxiv.org/abs/1810.04186
We examine the formation of baryon-induced cores in the dark matter haloes of dwarf galaxies simulated with the EAGLE model of galaxy formation. As in earlier work, we find that the star formation gas density threshold plays a critical role. At low thresholds, baryons are unable to collapse to high enough density to dominate the gravitational potential before being dispersed by the energetic feedback of evolving stars. They therefore have little effect on the dark matter, even in systems with extended and bursty star formation, two ingredients often cited as critical for core formation. At higher thresholds, baryons collapse to densities comparable to the dark matter before being suddenly ejected by feedback, reducing the central dark matter density. At very high thresholds, cores do not form because the EAGLE feedback scheme is unable to remove baryons from the centre of dwarf galaxies. Core formation requires that baryons collect at the centre over a relatively long period of time, as this allows the halo to contract before baryons are expelled, maximizing the effect. Core formation thus occurs in a small number of distinctive gas blowouts. Short fluctuations, such as those associated with bursty star formation, are ineffective at altering the dark matter inner profile. Cores can also be erased if subsequent accretion allows the halo to contract. The inner dark matter content of low-mass haloes (and the size of their cores) is therefore very sensitive to the assumed threshold in the EAGLE model, hindering robust model predictions and the interpretation of observational data. A simulation of a $(12 \rm \ Mpc)^3$ cosmological volume with a high threshold results in dwarfs with sizeable cores over a limited halo mass range, but insufficient variety in mass profiles to explain the observed diversity of dwarf galaxy rotation curves.
A. Benitez-Llambay, C. Frenk, A. Ludlow, et. al.
Thu, 11 Oct 18
47/72
Comments: 18 pages, Submitted to MNRAS