Alas, the dark matter structures were not that trivial
TL;DR: In this article, it was shown that the radial variation of the mass profile, dispersion profile, etc. is not a simple power law in radius, with the "golden values" = 3 and d = r (i.e., the phase-space density is only dependent on the radial component of the velocity dispersion).
Abstract: The radial density profile of dark matter structures has been observed to have an almost universal behavior in numerical simulations; however, the physical reason for this behavior remains unclear. It has previously been shown that if the pseudo phase-space density, ρ/σd, is a beautifully simple power law in radius, with the "golden values" = 3 and d = r (i.e., the phase-space density is only dependent on the radial component of the velocity dispersion), then one can analytically derive the radial variation of the mass profile, dispersion profile, etc. That would imply, if correct, that we just have to explain why ρ/σr3 ~ r−α, and then we would understand everything about equilibrated DM structures. Here we use a set of simulated galaxies and clusters of galaxies to demonstrate that there are no such golden values, but that each structure instead has its own set of values. Considering the same structure at different redshifts shows no evolution of the phase-space parameters toward fixed points. There is also no clear connection between the halo virialized mass and these parameters. This implies that we still do not understand the origin of the profiles of dark matter structures.
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TL;DR: In this paper, the authors explore the effects of the free streaming of warm dark matter particles on the formation of galaxies and find that the size of the core obtained in simulated haloes is in good agreement with theoretical expectations based on Liouville's theorem.
Abstract: The free streaming of warm dark matter particles dampens the fluctuation spectrum, flattens the mass function of haloes and imprints a fine grained phase density limit for dark matter structures. The phase space density limit is expected to imprint a constant density core at the halo center on the contrary to what happens for cold dark matter. We explore these effects using high resolution simulations of structure formation in different warm dark matter scenarios. We find that the size of the core we obtain in simulated haloes is in good agreement with theoretical expectations based on Liouville’s theorem. However, our simulations show that in order to create a significant core, (rc � 1 kpc), in a dwarf galaxy (M � 10 10 M⊙), a thermal candidate with a mass as low as 0.1 keV is required. This would fully prevent the formation of the dwarf galaxy in the first place. For candidates satisfying large scale structure constrains (m� larger than � 1 2 keV) the expected size of the core is of the order of 40 (80) pc for a dark matter halo with a mass of 10 10 (10 8 ) M⊙. We conclude that “standard” warm dark matter is not viable solution for explaining the presence of cored density profiles in low mass galaxies.
254 citations
Cites result from "Alas, the dark matter structures we..."
...On the other hand the CDM pseudo phase-space distribution is well fitted by a single power law profile on the whole range, in agreement with previous results (Taylor & Navarro 2001; Schmidt et al 2008)....
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TL;DR: A review of the current state of the art of cosmological dark matter simulations, with particular emphasis on the implications for dark matter detection efforts and studies of dark energy is presented in this article.
217 citations
INAF1, European Southern Observatory2, University of Copenhagen3, Johns Hopkins University4, Carnegie Institution for Science5, Academia Sinica6, Space Telescope Science Institute7, Heidelberg University8, University of Vienna9, University of Milan10, Paris Observatory11, Spanish National Research Council12, University of the Basque Country13, University of Concepción14, Michigan State University15, Princeton University16, University of California, Berkeley17, Ohio State University18, California Institute of Technology19, CERN20, Max Planck Society21
TL;DR: In this article, the mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z = 0.44 CLASH cluster MACS J1206.2-0847 were derived using the projected phase-space distribution of cluster galaxies.
Abstract: Aims. We constrain the mass, velocity-anisotropy, and pseudo-phase-space
density profiles of the z = 0.44 CLASH cluster MACS J1206.2-0847, using the projected phase-space
distribution of cluster galaxies in combination with gravitational lensing.Methods. We use an unprecedented data-set of ≃600 redshifts for cluster
members, obtained as part of a VLT/VIMOS large program, to constrain the cluster mass
profile over the radial range ~0–5 Mpc (0–2.5 virial radii) using the MAMPOSSt and Caustic
methods. We then add external constraints from our previous gravitational lensing
analysis. We invert the Jeans equation to obtain the velocity-anisotropy profiles of
cluster members. With the mass-density and velocity-anisotropy profiles we then obtain the
first determination of a cluster pseudo-phase-space density profile.Results. The kinematics and lensing determinations of the cluster mass
profile are in excellent agreement. This is very well fitted by a NFW model with mass
M200 = (1.4 ± 0.2) × 1015 M⊙
and concentration c200 = 6 ± 1, only slightly higher than
theoretical expectations. Other mass profile models also provide acceptable fits to our
data, of (slightly) lower (Burkert, Hernquist, and Softened Isothermal Sphere) or
comparable (Einasto) quality than NFW. The velocity anisotropy profiles of the passive and
star-forming cluster members are similar, close to isotropic near the center and
increasingly radial outside. Passive cluster members follow extremely well the theoretical
expectations for the pseudo-phase-space density profile and the relation between the slope
of the mass-density profile and the velocity anisotropy. Star-forming cluster members show
marginal deviations from theoretical expectations.Conclusions. This is the most accurate determination of a cluster mass
profile out to a radius of 5 Mpc, and the only determination of the velocity-anisotropy
and pseudo-phase-space density profiles of both passive and star-forming galaxies for an
individual cluster. These profiles provide constraints on the dynamical history of the
cluster and its galaxies. Prospects for extending this analysis to a larger cluster sample
are discussed.
193 citations
TL;DR: In this article, the authors examine assembly bias for the halo properties: shape, triaxiality, concentration, spin, shape of the velocity ellipsoid, and velocity anisotropy.
Abstract: Based on the Millennium Simulation we examine assembly bias for the halo properties: shape, triaxiality, concentration, spin, shape of the velocity ellipsoid, and velocity anisotropy. For consistency, we determine all these properties using the same set of particles, namely all gravitationally self-bound particles belonging to the most massive substructure of a given friends-of-friends halo. We confirm that near-spherical and high-spin halos show enhanced clustering. The opposite is true for strongly aspherical and low-spin halos. Further, below the typical collapse mass, M *, more concentrated halos show stronger clustering, whereas less concentrated halos are less clustered which is reversed for masses above M *. Going beyond earlier work we show that: (1) oblate halos are more strongly clustered than prolate ones; (2) the dependence of clustering on the shape of the velocity ellipsoid coincides with that of the real-space shape, although the signal is stronger; (3) halos with weak velocity anisotropy are more clustered, whereas radially anisotropic halos are more weakly clustered; (4) for all highly clustered subsets we find systematically less radially biased velocity anisotropy profiles. These findings indicate that the velocity structure of halos is tightly correlated with environment.
119 citations
Cites background or methods from "Alas, the dark matter structures we..."
...Motivated by studies of Hansen et al. (2006) and Schmidt et al. (2008) we also probe the behavior for phase space densities computed as ρ/σ3r , where σr denotes the radial velocity dispersion....
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...Schmidt et al. (2008) argued that there is no empirical justification (but see also Dehnen & McLaughlin 2005) for the particular definition of phase space density used here, and we find that changing the exponent of the velocity dispersion definitely has an impact on the correlation between…...
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01 Jan 2013
TL;DR: In this paper, the mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z = 0.44 CLASH cluster MACS J1206.2-0847 were derived using the projected phase-space distribution of cluster galaxies.
Abstract: Aims. We constrain the mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z = 0.44 CLASH cluster MACS J1206.2-0847, using the projected phase-space distribution of cluster galaxies in combination with gravitational lensing. Methods. We use an unprecedented data-set of � 600 redshifts for cluster members, obtained as part of a VLT/VIMOS large program, to constrain the cluster mass profile over the radial range ∼0‐5 Mpc (0‐2.5 virial radii) using the MAMPOSSt and Caustic methods. We then add external constraints from our previous gravitational lensing analysis. We invert the Jeans equation to obtain the velocity-anisotropy profiles of cluster members. With the mass-density and velocity-anisotropy profiles we then obtain the first determination of a cluster pseudo-phase-space density profile. Results. The kinematics and lensing determinations of the cluster mass profile are in excellent agreement. This is very well fitted by a NFW model
105 citations
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TL;DR: There is a deep and useful connection between statistical mechanics and multivariate or combinatorial optimization (finding the minimum of a given function depending on many parameters), and a detailed analogy with annealing in solids provides a framework for optimization of very large and complex systems.
Abstract: There is a deep and useful connection between statistical mechanics (the behavior of systems with many degrees of freedom in thermal equilibrium at a finite temperature) and multivariate or combinatorial optimization (finding the minimum of a given function depending on many parameters). A detailed analogy with annealing in solids provides a framework for optimization of the properties of very large and complex systems. This connection to statistical mechanics exposes new information and provides an unfamiliar perspective on traditional optimization problems and methods.
41,772 citations
TL;DR: In this article, a modified Monte Carlo integration over configuration space is used to investigate the properties of a two-dimensional rigid-sphere system with a set of interacting individual molecules, and the results are compared to free volume equations of state and a four-term virial coefficient expansion.
Abstract: A general method, suitable for fast computing machines, for investigating such properties as equations of state for substances consisting of interacting individual molecules is described. The method consists of a modified Monte Carlo integration over configuration space. Results for the two‐dimensional rigid‐sphere system have been obtained on the Los Alamos MANIAC and are presented here. These results are compared to the free volume equation of state and to a four‐term virial coefficient expansion.
35,161 citations
"Alas, the dark matter structures we..." refers methods in this paper
...Since there is the possibility of local minima in the ’χ2-landscape’ we have implemented the metropolis choice in our code (Metropolis et al. 1953)....
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TL;DR: In this article, high-resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple universal profile.
Abstract: High resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple “universal” profile. Regardless of their mass, halos are nearly isothermal over a large range in radius, but significantly shallower than r -2 near the center and steeper than r -2 in the outer regions. The characteristic overdensity of a halo correlates strongly with halo mass in a manner consistent with the mass dependence of the epoch of halo formation. Matching the shape of the rotation curves of disk galaxies with this halo structure requires (i) disk mass-to-light ratios to increase systematically with luminosity, (ii) halo circular velocities to be systematically lower than the disk rotation speed, and (iii) that the masses of halos surrounding bright galaxies depend only weakly on galaxy luminosity. This offers an attractive explanation for the puzzling lack of correlation between luminosity and dynamics in observed samples of binary galaxies and of satellite companions of bright spiral galaxies, suggesting that the structure of dark matter halos surrounding bright spirals is similar to that of cold dark matter halos.
7,622 citations
"Alas, the dark matter structures we..." refers result in this paper
...…with a fairly shallow profile in the central region,γ ≡ dlnρ/dlnr ∼ −1 (or maybe zero), to something steeper in the outer region, γ ∼ −3 (or maybe steeper) (Navarro et al. 1996; Moore et al. 1998; Diemand et al. 2007) (see also Reed et al. (2003); Stoehr (2004); Navarro et al. (2004); Graham…...
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...The most simple analytical solutions to this problem showed, that the density slopes could vary in the range from -1 to -3 (Hansen 2004), in excellent agreement with numerical results of Navarro et al. (1996)....
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TL;DR: In this paper, gas and total mass profiles for 13 low-redshift, relaxed clusters spanning a temperature range 0.7-9 keV were derived from all available Chandra data of sufficient quality.
Abstract: We present gas and total mass profiles for 13 low-redshift, relaxed clusters spanning a temperature range 0.7-9 keV, derived from all available Chandra data of sufficient quality. In all clusters, gas-temperature profiles are measured to large radii (Vikhlinin et al.) so that direct hydrostatic mass estimates are possible to nearly r500 or beyond. The gas density was accurately traced to larger radii; its profile is not described well by a beta model, showing continuous steepening with radius. The derived ρtot profiles and their scaling with mass generally follow the Navarro-Frenk-White model with concentration expected for dark matter halos in ΛCDM cosmology. However, in three cool clusters, we detect a central mass component in excess of the Navarro-Frenk-White profile, apparently associated with their cD galaxies. In the inner region (r < 0.1r500), the gas density and temperature profiles exhibit significant scatter and trends with mass, but they become nearly self-similar at larger radii. Correspondingly, we find that the slope of the mass-temperature relation for these relaxed clusters is in good agreement with the simple self-similar behavior, M500 Tα, where α = (1.5-1.6) ± 0.1, if the gas temperatures are measured excluding the central cool cores. The normalization of this M-T relation is significantly, by ≈30%, higher than most previous X-ray determinations. We derive accurate gas mass fraction profiles, which show an increase with both radius and cluster mass. The enclosed fgas profiles within r2500 0.4r500 have not yet reached any asymptotic value and are still far (by a factor of 1.5-2) from the universal baryon fraction according to the cosmic microwave background (CMB) observations. The fgas trends become weaker and its values closer to universal at larger radii, in particular, in spherical shells r2500 < r < r500.
1,448 citations
TL;DR: In this article, gas and total mass profiles for 13 low-redshift, relaxed clusters spanning a temperature range 0.7-9 keV were derived from all available Chandra data of sufficient quality.
Abstract: We present gas and total mass profiles for 13 low-redshift, relaxed clusters spanning a temperature range 0.7-9 keV, derived from all available Chandra data of sufficient quality. In all clusters, gas temperature profiles are measured to large radii (Vikhlinin et al.) so that direct hydrostatic mass estimates are possible to nearly r_500 or beyond. The gas density was accurately traced to larger radii; its profile is not described well by a beta-model, showing continuous steepening with radius. The derived rho_tot profiles and their scaling with mass generally follow the Navarro-Frenk-White model with concentration expected for dark matter halos in LambdaCDM cosmology. In the inner region (r<0.1r_500), the gas density and temperature profiles exhibit significant scatter and trends with mass, but they become nearly self-similar at larger radii. Correspondingly, we find that the slope of the mass-temperature relation for these relaxed clusters is in good agreement with the simple self-similar behavior, M_500 ~ T^alpha, where alpha=(1.5-1.6)+-0.1, if the gas temperatures are measured excluding the central cool cores. The normalization of this M-T relation is significantly, by =~ 30%, higher than most previous X-ray determinations. We derive accurate gas mass fraction profiles, which show increase both with radius and cluster mass. The enclosed f_gas profiles within r_2500 =~ 0.4 r_500 have not yet reached any asymptotic value and are still far (by a factor of 1.5-2) from the Universal baryon fraction according to the CMB observations. The f_gas trends become weaker and its values closer to Universal at larger radii, in particular, in spherical shells r_2500
1,325 citations
"Alas, the dark matter structures we..." refers background in this paper
...…and observations concerning the central steepness (Pointecouteau et al. 2005; Sand et al. 2004; Buote & Lewis 2004; Broadhurst et al. 2005; Vikhlinin et al. 2006), however, for smaller structures, like galaxies or dwarf galaxies, observations tend to indicate central cores (Salucci et…...
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