Freezing and melting: the origin and destruction of universal dark matter cusps through maximum entropy principles

Andrew Pontzen

October 18, 2012

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Abstract: I review some recent developments in attempting to reconcile the observed galaxy population with numerical models of structure formation in the ‘LCDM’ concordance cosmology. Focussing on behaviour of dwarf galaxies, I describe the infamous ‘cusp-core’ dichotomy — a long-standing challenge to the LCDM picture on small scales — and use toy models to show how it is resolved in recent numerical simulations (Pontzen & Governato 2012). I then discuss the current observational status of this picture (Teyssier, Pontzen & Read 2012; Penarrubia et al 2012). In the second half of the talk, I apply the analytic techniques developed for probing the effect of gas on dark matter dynamics to the question of how, in the absence of baryons, a universal “NFW” dark matter halo profile emerges (independent of scale or details of the initial conditions). Thus the generation of NFW halos on the one hand and the destruction of their central cusps on the other can be ascribed to surprisingly similar physical arguments.