Year: 2007
Type: article
Abstract: The evolution of the phase-space density profile in dark matter (DM) halos is investigated by means of constrained simulations, designed to control the merging history of a given DM halo. Halos evolve through a series of quiescent phases of a slow accretion intermitted by violent events of major mergers. In the quiescent phases the density of the halo closely follows the NFW profile and the phase-space density profile, Q ( r ) , is given by the Taylor & Navarro power law, r −β , where β ≈ 1.9 and stays remarkably stable over the Hubble time. Expressing the phase-space density by the NFW parameters, Q ( r ) = Q s ( r / R s ) −β , the evolution of Q is determined by Q s . We have found that the effective mass surface density within R s , Σ s ≡ ρ s R s , remains constant throughout the evolution of a given DM halo along the main branch of its merging tree. This invariance entails that Q s ∝ R s −5/2 and Q ( r ) ∝ Σ s −1/2 R s −5/2 ( r / R s ) −β . It follows that the phase-space density remains constant, in the sense of Q s = const ., in the quiescent phases and it decreases as R s −5/2 in the violent ones. The physical origin of the NFW density profile and the phase-space density power law is still unknown. Yet, the numerical experiments show that halos recover these relations after the violent phases. The major mergers drive R s to increase and Q s to decrease discontinuously while keeping Q s × R s 5/2 = const . The virial equilibrium in the quiescent phases implies that a DM halos evolves along a sequence of NFW profiles with constant energy per unit volume (i.e., pressure) within R s .
Source: The Astrophysical Journal
DOI: 10.1086/523695
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W1991684589