Small scale clustering of late forming dark matter
Pier Stefano Corasaniti2015, Physical Review D
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Abstract
We perform a study of the nonlinear clustering of matter in the late-forming dark matter (LFDM) scenario in which dark matter results from the transition of a nonminimally coupled scalar field from radiation to collisionless matter. A distinct feature of this model is the presence of a damped oscillatory cutoff in the linear matter power spectrum at small scales. We use a suite of high-resolution N-body simulations to study the imprints of LFDM on the nonlinear matter power spectrum, the halo mass and velocity functions and the halo density profiles. The model largely satisfies highredshift matter power spectrum constraints from Lyman-α forest measurements, while it predicts suppressed abundance of low-mass halos (∼ 10 9 -10 10 h -1 M ) at all redshifts compared to a vanilla ΛCDM model. The analysis of the LFDM halo velocity function shows a better agreement than the ΛCDM prediction with the observed abundance of low-velocity galaxies in the local volume. Halos with mass M 10 11 h -1 M show minor departures of the density profiles from ΛCDM expectations, while smaller-mass halos are less dense, consistent with the fact that they form later than their ΛCDM counterparts.
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Mass growth and density profiles of dark matter haloes in hierarchical clustering
Monthly Notices of the Royal Astronomical Society, 1999
We develop a model for the growth of dark matter halos and use it to study their evolved density profiles. In this model, halos are spherical and form by quiescent accretion of matter in clumps, called satellites. The halo mass as a function of redshift is given by the mass of the most massive progenitor, and is determined from Monte-Carlo realizations of the merger-history tree. Inside the halo, satellites move under the action of the gravitational force of the halo and a dynamical friction drag force. The associated equation of motion is solved numerically. The energy lost to dynamical friction is transferred to the halo in the form of kinetic energy. As they sink into the halo, satellites continually lose matter as a result of tidal stripping. The stripped matter moves inside the halo free of dynamical friction. The evolved density profiles are steeper than those obtained by assuming that, once they have been accreted onto the parent halo, satellites remain at a fixed distance from the halo center. We find that the final density profile depends mainly on the rate of infall of matter onto the halo. This, in turn, depends on the initial fluctuation field as well as on cosmology. For mass scales where the effective spectral index of the initial density field is less than −1, the model predicts a profile which can only approximately be matched by the one parameter family of curves suggested by Navarro, Frenk and White (1997). For scale-free power-spectra with initial slope n, the density profile within about 1% of the virial radius is ρ ∝ r −β , with 3(3 + n)/(5 + n) ≤ β ≤ 3(3 + n)/(4 + n).
Mass growth and density profiles of dark matter halos in hierarchical clustering
1998
We develop a model for the growth of dark matter halos and use it to study their evolved density profiles. In this model, halos are spherical and form by quiescent accretion of matter in clumps, called satellites. The halo mass as a function of redshift is given by the mass of the most massive progenitor, and is determined from Monte-Carlo realizations of the merger-history tree. Inside the halo, satellites move under the action of the gravitational force of the halo and a dynamical friction drag force. The associated equation of motion is solved numerically. The energy lost to dynamical friction is transferred to the halo in the form of kinetic energy. As they sink into the halo, satellites continually lose matter as a result of tidal stripping. The stripped matter moves inside the halo free of dynamical friction. The evolved density profiles are steeper than those obtained by assuming that, once they have been accreted onto the parent halo, satellites remain at a fixed distance from the halo center. We find that the final density profile depends mainly on the rate of infall of matter onto the halo. This, in turn, depends on the initial fluctuation field as well as on cosmology. For mass scales where the effective spectral index of the initial density field is less than -1, the model predicts a profile which can only approximately be matched by the one parameter family of curves suggested by Navarro, Frenk and White (1997). For scale-free power-spectra with initial slope $n$, the density profile within about 1% of the virial radius is $\rho\propto r^{-\beta}$, with $3(3+n)/(5+n)\le\beta\le 3(3+n)/(4+n)$.
The phase-space density distribution of dark matter halos
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On the Structure of Dark Matter Halos at the Damping Scale of the Power Spectrum with and without Relict Velocities
Astrophysical Journal, 2008
We report a series of high-resolution cosmological N-body simulations designed to explore the formation and properties of dark matter halos with masses close to the damping scale of the primordial power spectrum of density fluctuations. We further investigate the effect that the addition of a random component, v rms , into the particle velocity field has on the structure of halos. We adopted as a fiducial model the Λ warm dark matter (ΛWDM) cosmology with a non-thermal sterile neutrino mass of 0.5 keV. The filtering mass corresponds then to M f = 2.6 × 10 12 h −1 M ⊙ . Halos of masses close to M f were simulated with several million of particles. The results show that, on one hand, the inner density slope of these halos (at radii < ∼ 0.02 the virial radius R v ) is systematically steeper than the one corresponding to the Navarro-Frenk-White (NFW) fit or to the cold dark matter counterpart. On the other hand, the overall density profile (radii larger than 0.02 R v ) is less curved and less concentrated than the NFW fit, with an outer slope shallower than -3. For simulations with v rms , the inner halo density profiles flatten significantly at radii smaller than 2-3 h −1 kpc ( < ∼ 0.010R v − 0.015R v ). A constant density core is not detected in our simulations, with the exception of one halo for which the flat core radius is ≈ 1h −1 kpc. Nevertheless, if "cored" density profiles are used to fit the halo profiles, the inferred core radii are ≈ (0.1 − 0.8)h −1 kpc, in rough agreement with theoretical predictions based on phase-space constrains, and on dynamical models of warm gravitational collapse. A reduction of v rms by a factor of 3 produces a modest decrease in core radii, less than a factor of 1.5. We discuss the extension of our results into several contexts, for example, to the structure of the cold DM micro-halos at the damping scale of this model.
The Shape of Dark Matter Halos: Dependence on Mass, Redshift, Radius, and Formation
Monthly Notices of The Royal Astronomical Society, 2005
Using six high resolution dissipationless simulations with a varying box size in a flat LCDM universe, we study the mass and redshift dependence of dark matter halo shapes for M_vir = 9.0e11 - 2.0e14, over the redshift range z=0-3, and for two values of sigma_8=0.75 and 0.9. Remarkably, we find that the redshift, mass, and sigma_8 dependence of the mean smallest-to-largest axis ratio of halos is well described by the simple power-law relation <s> = (0.54 +- 0.02)(M_vir/M_*)^(-0.050 +- 0.003), where s is measured at 0.3 R_vir and the z and sigma_8 dependences are governed by the characteristic nonlinear mass, M_*=M_*(z,sigma_8). We find that the scatter about the mean s is well described by a Gaussian with sigma ~ 0.1, for all masses and redshifts. We compare our results to a variety of previous works on halo shapes and find that reported differences between studies are primarily explained by differences in their methodologies. We address the evolutionary aspects of individual halo shapes by following the shapes of the halos through ~100 snapshots in time. We determine the formation scalefactor a_c as defined by Wechsler et al. (2002) and find that it can be related to the halo shape at z = 0 and its evolution over time.
Phase-Space Evolution of Dark Matter Halos
2007
(Context) In a Universe dominated by dark matter, halos are continuously accreting mass (violently or not) and such mechanism affects their dynamical state. (Aims) The evolution of dark matter halos in phase-space, and using the phase-space density indicator Q=rho/sigma^3 as a tracer, is discussed. (Methods) We have performed cosmological N-body simulations from which we have carried a detailed study of the evolution of ~35 dark halos in the interval 0<z<10. (Results)The follow up of individual halos indicates two distinct evolutionary phases. First, an early and fast decrease of Q associated to virialization after the gravitational collapse takes place. The nice agreement between simulated data and theoretical expectations based on the spherical collapse model support such a conjecture. The late and long period where a slow decrease of the phase-space density occurs is related to accretion and merger episodes. The study of some merger events in the phase-space (radial velocity versus radial distance) reveals the formation of structures quite similar to caustics generated in secondary infall models of halo formation. After mixing in phase-space, halos in quasi-equilibrium have flat-topped velocity distributions (negative kurtosis) with respect to Gaussians. The effect is more noticiable for captured satellites and/or substructures than for the host halo.
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EAS Publications Series, 2006
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Monthly Notices of the Royal Astronomical Society, 2003
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The Central Mass and Phase-Space Densities of Dark Matter Halos: Cosmological Implications
The Astrophysical Journal, 2002
Current data suggest that the central mass densities ρ 0 and phase-space densities Q ≡ ρ 0 /σ 3 V of cosmological halos in the present universe are correlated with their velocity dispersions σ V over a very wide range of σ V from less than 10 to more than 1000 km s −1 . Such correlations are an expected consequence of the statistical correlation of the formation epochs of virialized objects in the CDM model with their masses; the smaller-mass halos typically form first and merge to form larger-mass halos later. We have derived the Q − σ V and ρ 0 − σ V correlations for different CDM cosmologies and compared the predicted correlations with the observed properties of a sample of low-redshift halos ranging in size from dwarf spheroidal galaxies to galaxy clusters. Our predictions are generally consistent with the data, with preference for the currently-favored, flat ΛCDM model. Such a comparison serves to test the basic CDM paradigm while constraining the background cosmology and the power-spectrum of primordial density fluctuations, including larger wavenumbers than have previously been constrained.
Dark matter haloes within clusters
Monthly Notices of the Royal Astronomical Society, 1998
We examine the properties of dark matter halos within a rich galaxy cluster using a high resolution simulation that captures the cosmological context of a cold dark matter universe. The mass and force resolution permit the resolution of 150 halos with circular velocities larger than 80 km s −1 within the cluster's virial radius of 2 Mpc. This enables an unprecedented study of the statistical properties of a large sample of dark matter halos evolving in a dense environment. The cumulative fraction of mass attached to these halos varies from 0% at 200 kpc, to 13% at the virial radius. Even at this resolution the overmerging problem persists; halos that pass within 200 kpc of the cluster center are tidally disrupted. Additional substructure is lost at earlier epochs within the massive progenitor halos. The median ratio of apocentric to pericentric radii is 6:1; the orbital distribution is close to isotropic, circular orbits are rare, radial orbits are common. The orbits of halos are unbiased with respect to both position within the cluster and with the orbits of the smooth dark matter background and no velocity bias is detected. The tidal radii of surviving halos are generally well-fit using the simple analytic prediction applied to their orbital pericenters. Halos within clusters have higher concentrations than those in the field. Within the cluster, halo density profiles can be modified by tidal forces and individual encounters with other halos that cause significant mass loss -"galaxy harassment". Mergers between halos do not occur inside the clusters virial radius.
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Monthly Notices of The Royal Astronomical Society, 2006
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Astrophysical Journal, 2006
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We use N -body simulations to investigate the structure and dynamical evolution of dark matter halos in clusters of galaxies. Our sample consists of nine massive halos from an Einstein-De Sitter universe with scale free power spectrum and spectral index n = -1. Halos are resolved by 20000 particles each, on average, and have a dynamical resolution of 20-25 kpc, as shown by extensive tests. Large scale tidal fields are included up to a scale L = 150 Mpc using background particles. We find that the halo formation process can be characterized by the alternation of two dynamical configurations: a merging phase and a relaxation phase, defined by their signature on the evolution of the total mass and root mean square (rms) velocity. Halos spend on average one third of their evolution in the merging phase and two thirds in the relaxation phase. Using this definition, we study the density profiles and show how they change during the halo dynamical history. In particular, we find that the average density profiles of our halos are fitted by the Navarro, Frenk & White (1995) analytical model with an rms residual of 17% between the virial radius R v and 0.01R v . The Hernquist (1990) analytical density profiles fits the same halos with an rms residual of 26%. The trend with mass of the scale radius of these fits is marginally consistent with that found by : compared to their results our halos are more centrally concentrated, and the relation between scale radius and halo mass is slightly steeper. We find a moderately large scatter in this relation, due both to dynamical evolution within halos and to fluctuations in the halo population. We analyze the dynamical equilibrium of our halos using the Jeans' equation, and find that on average they are approximately in equilibrium within their virial radius. Finally, we find that the projected mass profiles of our simulated halos are in very good agreement with the profiles of three rich galaxy clusters derived from strong and weak gravitational lensing observations.
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Monthly Notices of the Royal Astronomical Society, 1997
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Monthly Notices of the Royal Astronomical Society, 2014
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