Nonextensive Theory of Dark Matter and Gas Density Profiles

Abstract

Pronounced core-halo patterns of dark matter and gas density profiles, observed in relaxed galaxies and clusters, were hitherto fitted by empirical power laws. On the other hand, similar features are well known from astrophysical plasma environments, subject to long-range interactions, modeled in the context of a nonextensive entropy generalization. We link nonextensive statistics to the problem of density distributions in large-scale structures and provide fundamentally derived density profiles, representing accurately the characteristics of both dark matter and hot plasma distributions as observed or generated in simulations. The bifurcation of the density distribution into a kinetic dark matter/thermodynamic gas branch turns out to be a natural consequence of the theory and is controlled by a single parameter, κ, measuring physically the degree of coupling within the system. Consequently, it is proposed to favor nonextensive distributions, derived from the fundamental physical context of entropy generalization and accounting for nonlocality and long-range interactions in gravitationally coupled systems, when modeling observed density profiles of astrophysical structures.