Generating Equilibrium Dark Matter Halos: Inadequacies of the Local Maxwellian Approximation

By S. Kazantzidis, J. Magorrian, B. Moore. 2003

207 citations recorded by the source corpus.

We describe an algorithm for constructing N-body realizations of equilibrium spherical systems. A general form for the mass density ρ is used, making it possible to represent most of the popular density profiles found in the literature, including the cuspy density profiles found in high-resolution cosmological simulations. We demonstrate explicitly that our models are in equilibrium. In contrast, many existing N-body realizations of isolated systems have been constructed under the assumption that the local velocity distribution is Maxwellian. We show that a Maxwellian halo with an initial ρ(r) ∝ r-1 central density cusp immediately develops a constant-density core. Moreover, after just one crossing time the orbital anisotropy has changed over the entire system, and the initially isotropic model becomes radially anisotropic. These effects have important implications for many studies, including the survival of substructure in cold dark matter (CDM) models. Comparing the evolution and mass-loss rate of isotropic Maxwellian and self-consistent Navarro, Frenk, & White (NFW), satellites orbiting inside a static host CDM potential, we find that the former are unrealistically susceptible to tidal disruption. Thus, recent studies of the mass-loss rate and disruption timescales of substructure in CDM models may be compromised by using the Maxwellian approximation. We also demonstrate that a radially anisotropic, self-consistent NFW satellite loses mass at a rate several times higher than that of its isotropic counterpart on the same external tidal field and orbit.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/6ef66ffb69e022d81a347b78c24000f58330d032

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Citations in the corpus

The impact of dark matter cusps and cores on the satellite galaxy population around spiral galaxies (2010, background): “To avoid that problem, Kazantzidis et al. (2004) impose a truncation at Rvir that can be written as ρ(r) = ρ0 Cγvir(1 + C α vir) (β−γ)/α ( r Rvir ) exp ( − r −Rvir Rdec ) (r > Rvir); (4) where Rdec is a small quantity, whose value we choose as 0.1Rvir.”
The Physics of Galaxy Clustering. I. A Model for Subhalo Populations (2004, methodology): “Some of the inputs for the evolution of subhalos is provided by controlled (non-cosmological) simulations (e.g., Colpi, Mayer, & Governato 1999; Velázquez & White 1999; Taylor & Babul 2001; Mayer et al. 2002; Hashimoto et al. 2003; Taffoni et al. 2003; Kazantzidis et al. 2004b).”
The tidal stripping of satellites (2005, methodology): “We note here that using distribution functions rather than the more familiar Maxwellian approximation (as in Hernquist 1993) for calculating particle velocities is much more accurate for simulations of tidal stripping (Kazantzidis et al. 2004).”
Resolving the Formation of Protogalaxies. I. Virialization (2007, background): “Halo and Filament Contrasts The dark matter velocity distributions are typical of a virialized system with the majority of the matter having a Maxwellian distribution with a dispersion corresponding to the main halo (Boylan-Kolchin & Ma 2004; Dieman et al. 2004; Kazantzidis et al. 2004).”
Does the Fornax dwarf spheroidal have a central cusp or core (2006, background): “Of course this assumption does not hold, but is good enough for our purposes (Kazantzidis et al. 2004).”
Equilibrium Disk-Bulge-Halo Models for the Milky Way and Andromeda Galaxies (2005, methodology): “Moreover, the models readjust to a state different from the one proposed (see, e.g., Kazantzidis et al. 2004).”
The Tumultuous Lives of Galactic Dwarfs and the Missing Satellites Problem (2004, result): “A similar result has been found by Kazantzidis et al. (2004) and Moore et al. (2003).”
Mass loss from dwarf spheroidal galaxies: the origins of shallow dark matter cores and exponential surface brightness profiles (2004, methodology): “To test that the results presented here are not affected by the Maxwellian approximation we resimulated one run using an initial condition generator which drew the velocities directly from a numerically calculated distribution function, as in Kazantzidis et al. (2004).”
Dark matter direct detection with non-Maxwellian velocity structure (2009, background): “Actually there is no reason to assume that a self-gravitating, dissipationless system would have a locally Maxwellian velocity distribution, and in fact it has been shown that self-consistent, stable models of cuspy DM structures require just such non-Gaussianity [30, 31].”
STIRRING UP THE POT: CAN COOLING FLOWS IN GALAXY CLUSTERS BE QUENCHED BY GAS SLOSHING? (2009, background): “It has been shown that this approach is not sufficient to accurately represent the velocity distribution functions of dark matter halos with a central cusp such as the NFW profile (Kazantzidis et al. 2004).”
Dynamical Blueprints for Galaxies (2008, methodology): “When used as initial conditions in N-body experiments, they readjust to a different state from the one proposed (see, e.g., Kazantzidis et al. 2004).”
Breathing in Low-Mass Galaxies: A Study of Episodic Star Formation (2007, background): “Equilibrium NFW dark matter halos with a concentration c = 8 were created following Kazantzidis et al. (2004), where c = rvir/rs, rvir is the virial radius and rs is the scale radius.”
Simulations of minor mergers - I. General properties of thick discs (2008, unknown): “We follow Kazantzidis et al. (2004) and compute numerically the DF that, in general, is given by5: f(Q) = 1√ 8π2 [ ∫ Q 0 d2ρhalo dψ2 dψ√ Q− ψ + 1√ Q ( dρhalo dψ ) ψ=0 ] (A11) (Binney & Tremaine 1987) where Q = ψ−v2/2; ψ = −Φ(r) is the effective gravitational potential (including the disk); and v is…”
The Causes of Halo Shape Changes Induced by Cooling Baryons: Disks versus Substructures (2007, methodology): “But this need not be in disagreement with CDM since the condensation of baryons to the centers of halos has been shown to lead to rounder halos (Dubinski 1994; Kazantzidis et al. 2004).”
Dark Matter Substructure in Numerical Simulations: A Tale of Discreteness Noise, Runaway Instabilities, and Artificial Disruption (2018, methodology): “To summarize, we confirm the conclusion of Kazantzidis et al. (2004b) that using the local Maxwellian approximation to initialize subhaloes results in excessive mass loss and premature, artificial disruption.”