On the Origin of the Inner Structure of Halos

Abstract

We calculate by means of the Press-Schechter formalism the density profile developed by dark-matter halos during accretion, i.e., the continuous aggregation of small clumps. We find that the shape of the predicted profile is similar to that shown by halos in high-resolution cosmological simulations. Furthermore, the mass-concentration relation is correctly reproduced at any redshift in all the hierarchical cosmologies analyzed, except for very large halo masses. The role of major mergers, which can cause the rearrangement of the halo structure through violent relaxation, is also investigated. We show that, as a result of the boundary conditions imposed by the matter continuously infalling into the halo during the violent relaxation process, the shape of the density profile emerging from major mergers is essentially identical to the shape the halo would have developed through pure accretion. This result explains why, according to high-resolution cosmological simulations, relaxed halos of a given mass have the same density profile regardless of whether they have had a recent merger or not, and why both spherical infall and hierarchical assembly lead to very similar density profiles. Finally, we demonstrate that the density profile of relaxed halos is not affected either by the capture of clumps of intermediate mass.Comment: 14 pages, 8 figures, accepted for publication in ApJ. Minor changes, matches the published version. To appear in the ApJ August 10, 2003 issu

The orbital velocity anisotropy of cluster galaxies: evolution

“…According to theoretical models, the growth of halo masses occurs in two phases, an initial, fast accretion phase, followed by a slower, smoother accretion phase (Lapi & Cavaliere 2009). During the fast accretion phase clusters undergo major mergers that can induce rapid changes in the cluster gravitational potential (Manrique et al 2003;Peirani et al 2006;Valluri et al 2007), causing energy and angular momentum mixing in the galaxy distributions, and thereby isotropization of galaxy orbits (Hénon 1964;Lynden-Bell 1967;Kandrup & Siopis 2003;Merritt 2005;Lapi & Cavaliere 2009). …”

The evolution of mass profiles of galaxy clusters

“…During the fast accretion phase clusters are subject to rapid variations of their gravitational potential [61,62,63], and these are capable of isotropizing galaxy orbits [64,65,66,67,46]. The end of the fast accretion phase for cluster-sized halos occurs at z ≈ 0.4 [46], hence it is not over yet for most of the clusters of our high-z sample.…”

CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of thez= 0.44 galaxy cluster MACS J1206.2-0847

“…Subramanian et al 2000; Thomas et al 2001;Salvador-Solé et al 2007), others have not (Huss et al 1999a;Wang & White 2009). A general consensus is growing that the universal NFW-like shape, at least in the central regions, is the result of the initial, fast assembly phase of halos (Huss et al 1999b;Manrique et al 2003;Arad et al 2004;Tasitsiomi et al 2004;Lu et al 2006;El-Zant 2008;Wang & White 2009;, characterized by dynamical processes such as violent and collective relaxation, and phase and chaotic mixing (Hénon 1964;Lynden-Bell 1967;Merritt 2005;Henriksen 2006, and references therein). The following slower accretion phase may be responsible for the outer slope of the density profile (Tasitsiomi et al 2004;Lu et al 2006;Hiotelis 2006).…”