Dark Matter Cusps and Cores by Violent Relaxation

We address both the long-standing puzzle of the origin of a universal cusp in dark-matter (DM) halos and the challenge introduced by new observational indications for a dearth of central DM and flat cores in a certain fraction of the galaxies. Such DM-deficient cores are reported both in massive galaxies at high redshifts and in dwarf galaxies, contrary to the expectations for a cusp based on current simulations within the standard LCDM cosmological scenario. We propose to better understand the structural evolution of DM halos in response to drastic mass changes and the gravitational interplay between the DM and the baryons, including inflows, mergers, tidal effects, and outflows. For this, we will develop our analytic model, CuspCore, which would provide a unified framework for following the violent relaxation of a halo after it has been perturbed from an equilibrium configuration. Utilizing this framework, we will work out a scenario for DM-deficient cores in high-z massive galaxies via DM ""heating"" by dynamical friction on compact merging satellites followed by DM expansion in response to AGN-driven outflows. The same framework will serve to generate cores in dwarf galaxies via supernova feedback and tidal stripping. Finally, we will attempt to use this framework to understand the original universal cuspy profile of DM halos based on non-adiabatic growth. Success in modeling the violent-relaxation process in these circumstances will be crucial for meeting the immediate challenges to the standard cosmological model, and it promises a general impact on other broad applications of galactic dynamics.""