Evolution of the phase-space density in dark matter halos

Yehuda Hoffman, Emilio Romano-Díaz, Isaac Shlosman, Clayton Heller

Research output: Contribution to journalArticlepeer-review

46 Scopus citations

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)-&beta, the evolution of Q is determined by Qs' We have found that the effective mass surface density within Rs, Σs = psRs, remains constant throughout the evolution of a given DM halo along the main branch of its merging tree. This invariance entails that Qs ∝ 'σ~1/2RS~5/2(r/Rs) . 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 Q s to decrease discontinuously while keeping Qs xR s5/2 = 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

Original languageEnglish
Pages (from-to)1108-1114
Number of pages7
JournalAstrophysical Journal
Volume671
Issue number2
DOIs
StatePublished - Dec 20 2007

Keywords

  • Dark matter
  • Galaxies: Interactions
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: halos
  • Galaxies: kinematics and dynamics

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