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) = Qs(r/Rs)−β, the evolution of Q is determined by Qs. We have found that the effective mass surface density within Rs, Σs ≡ ρsRs, remains constant throughout the evolution of a given DM halo along the main branch of its merging tree. This invariance entails that Qs ∝ Rs−5/2 and Q(r) ∝ Σs−1/2Rs−5/2(r/Rs)−β. It follows that the phase-space density remains constant, in the sense of Qs = const ., in the quiescent phases and it decreases as Rs−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 Rs to increase and Qs to decrease discontinuously while keeping Qs × Rs5/2 = 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 Rs.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.