Early flattening of dark matter cusps in dwarf spheroidal galaxies

Abstract

Simulations of the clustering of cold dark matter yield dark-matter halos that have central density cusps, but observations of totally dark-matter dominated dwarf spheroidal galaxies imply that they do not have cuspy central density profiles. We use analytic calculations and numerical modelling to argue that whenever stars form, central density cusps are likely to be erased. Gas that accumulates in the potential well of an initially cuspy dark-matter halo settles into a disc. Eventually the surface density of the gas exceeds the threshold for fragmentation into self-gravitating clouds. The clouds are massive enough to transfer energy to the darkmatter particles via dynamical friction on a short time-scale. The halo's central cusp is heated to form a core with central logarithmic density slope γ ≈ 0 before stellar feedback makes its impact. Since star formation is an inefficient process, the clouds are disrupted by feedback when only a small fraction of their mass has been converted to stars, and the dark matter dominates the final mass distribution.

A unified model for age–velocity dispersion relations in Local Group galaxies: disentangling ISM turbulence and latent dynamical heating

“…The same decrease in velocity dispersion may be expected for relaxation after potential reconfiguration due to feedback induced dark matter"cusp-core" transformations seen in simulations of low mass dwarf galaxies (Pontzen & Governato 2012;Di Cintio et al 2014;Read, Agertz & Collins 2016), or due to GMC based scouring (Nipoti & Binney 2015). Indeed Read, Agertz & Collins (2016) show not only is the core creation occurring in galaxies in the mass range of the dSphs, but that the velocity dispersion in their simulated cored galaxy may be lower by a factor of two than in the cuspy case.…”

Baryon-induced dark matter cores in the eagle simulations

“…Finally, we note that simulations by Read et al (2016Read et al ( , 2018 indicate that dark matter cusps may turn into cores even if the baryonic component had not been gravitationally dominant in the inner regions of the halo, in contrast with our results. As shown by El-Zant et al (2001), and more recently by Nipoti & Binney (2015), the transformation of a central cusp into a core could also be achieved through dynamical friction between dark matter and dense gaseous star-forming clumps that dominate the gravitational potential locally. These gaseous clumps are indeed present in the simulations by Read et al (2016), but not in ours.…”

A model for core formation in dark matter haloes and ultra-diffuse galaxies by outflow episodes

“…When a massive object such as a satellite galaxy or a clump of gas moves with respect to the dark matter background, it can transfer part of its kinetic energy to the background through dynamical friction, as the concentration of particles increases in its wake and generates a drag force (Chandrasekhar 1943). Dynamical friction can thus 'heat' the dark matter halo and contribute to remove the central cusp (El-Zant et al 2001Tonini et al 2006;Romano-Díaz et al 2008;Goerdt et al 2010;Cole et al 2011;Nipoti & Binney 2015). Alternatively, repeated gravitational potential fluctuations induced by stellar winds, supernova explosions and active galactic nuclei (AGNs) can also dynamically heat the dark matter and lead to the formation of a core (Dekel & Silk 1986;Read & Gilmore 2005;Mashchenko et al 2006Mashchenko et al , 2008Pontzen & Governato 2012, 2014Governato et al 2012;Zolotov et al 2012;Martizzi et al 2013;Teyssier et al 2013;Madau et al 2014;Dutton et al 2016b;El-Zant et al 2016;Peirani et al 2017).…”