Dynamical estimates of the local density of dark matter (original) (raw)
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Solar System constraints on local dark matter density
Journal of Cosmology and Astroparticle Physics, 2012
We study how the classical tests of general relativity are modified by the presence of a subdominant dark matter halo in the solar system. We use a general formalism to calculate the corrected expression for the relevant parameters, and obtain bound plots for the mean energy density and the dimension of the dark matter halo. Our results seem to favor a density profile peaked at the center of the solar system.
Journal of Physics G: Nuclear and Particle Physics, 2014
We present the recent robust determination of the value of the Dark Matter density at the Sun's location (ρ ⊙ ) with a technique that does not rely on a global mass-modeling of the Galaxy. The method is based on the local equation of centrifugal equilibrium and depends on local and quite well known quantities such as the angular Sun's velocity, the disk to dark contribution to the circular velocity at the Sun, and the thin stellar disk scale length. This determination is independent of the shape of the dark matter density profile, the knowledge of the rotation curve at any radius, and the very uncertain bulge/disk/dark-halo mass decomposition. The result is: ρ ⊙ = 0.43(0.11)(0.10) GeV/cm 3 , where the quoted uncertainties are due to the uncertainty a) in the slope of the circular-velocity at the Sun location and b) in the ratio between this radius and the exponential length scale of the stellar disk. The devised technique is also able to take into account any future improvement in the data relevant for the estimate.
The Core Density of Dark Matter Halos: A Critical Challenge to the ΛCDM Paradigm?
The Astrophysical Journal, 2000
We compare the central mass concentration of Cold Dark Matter halos found in cosmological N-body simulations with constraints derived from the Milky Way disk dynamics and from the Tully-Fisher relation. For currently favored values of the cosmological parameters (Ω 0 ∼ 0.3; Λ 0 = 1 − Ω 0 ∼ 0.7; h ∼ 0.7; COBE-and cluster abundance-normalized σ 8 ; Big-Bang nucleosynthesis Ω b ), we find that halos with circular velocities comparable to the rotation speed of the Galaxy have typically three times more dark matter inside the solar circle than inferred from observations of Galactic dynamics. Such high central concentrations of dark matter on the scale of galaxy disks also imply that stellar mass-to-light ratios much lower than expected from population synthesis models must be assumed in order to reproduce the zero-point of the Tully-Fisher relation. Indeed, even under the extreme assumption that all baryons in a dark halo are turned into stars, disks with conventional I-band stellar mass-to-light ratios (M/L I ∼ 2 ± 1(M/L I ) ⊙ ) are about two magnitudes fainter than observed at a given rotation speed. We examine several modifications to the ΛCDM model that may account for these discrepancies and conclude that agreement can only be accomplished at the expense of renouncing other major successes of the model. Reproducing the observed properties of disk galaxies thus appears to demand substantial revision to the currently most successful model of structure formation.
The dark matter density at the Sun's location
Astronomy & Astrophysics, 2010
We derive the value of the dark matter density at the Sun's location (rho_0) without globally mass-modeling the Galaxy. The proposed method relies on the local equation of centrifugal equilibrium and is independent of i) the shape of the dark matter density profile, ii) knowledge of the rotation curve from the galaxy center out to the virial radius, and iii) the uncertainties and the non-uniqueness of the bulge/disk/dark halo mass decomposition. The result can be obtained in analytic form. It explicitly includes the dependence on the relevant observational quantities and takes their uncertainties into account. By adopting the reference, state-of-the-art values for these, we find rho_0 = 0.43(11)(10)GeV/cm3, where the quoted uncertainties are respectively due to the uncertainty in the slope of the circular-velocity at the Sun location and the ratio between this radius and the length scale of the stellar exponential thin disk. We obtain a reliable estimate of rho_0, that, in addition, is ready to take into account any future change/improvement in the measures of the observational quantities it depends on.
The core density of dark matter halos: a critical challenge to the Lambda-CDM paradigm?
1999
We compare the central mass concentration of Cold Dark Matter halos found in cosmological N-body simulations with constraints derived from the Milky Way disk dynamics and from the Tully-Fisher relation. For currently favored values of the cosmological parameters ($\Omega_0 \sim 0.3$; Lambda0=1−Omega0sim0.7\Lambda_0=1-\Omega_0 \sim 0.7Lambda0=1−Omega0sim0.7; hsim0.7h \sim 0.7hsim0.7; COBE- and cluster abundance-normalized sigma8\sigma_8sigma8; Big-Bang nucleosynthesis Omegab\Omega_bOmegab), we find that halos with circular velocities comparable to the rotation speed of the Galaxy have typically {\it three times} more dark matter inside the solar circle than inferred from observations of Galactic dynamics. Such high central concentrations of dark matter on the scale of galaxy disks also imply that stellar mass-to-light ratios much lower than expected from population synthesis models must be assumed in order to reproduce the zero-point of the Tully-Fisher relation. Indeed, even under the extreme assumption that {\it all} baryons in a dark halo are turned into stars, disks with conventional III-band stellar mass-to-light ratios ($M/L_I \sim 2 \pm 1 (M/L_I)_{\odot}$) are about two magnitudes fainter than observed at a given rotation speed. We examine several modifications to the Lambda\LambdaLambdaCDM model that may account for these discrepancies and conclude that agreement can only be accomplished at the expense of renouncing other major successes of the model. Reproducing the observed properties of disk galaxies thus appears to demand substantial revision to the currently most successful model of structure formation.
Dark Matter Properties and Halo Central Densities
The Astrophysical Journal, 2002
Using an analytic model calibrated against numerical simulations, we calculate the central densities of dark matter halos in a "conventional" cold dark matter model with a cosmological constant (LCDM) and in a "tilted" model (TLCDM) with slightly modified parameters motivated by recent analyses of Lyα forest data. We also calculate how warm dark matter (WDM) would modify these predicted densities by delaying halo formation and imposing phase space constraints. As a measure of central density, we adopt the quantity ∆ V /2 , the density within the radius R V /2 at which the halo rotation curve falls to half of its maximum value, in units of the critical density. We compare the theoretical predictions to values of ∆ V /2 estimated from the rotation curves of dark matter dominated disk galaxies. Assuming that dark halos are described by NFW profiles, our results suggest that the conventional LCDM model predicts excessively high dark matter densities, unless there is some selection bias in the data toward the low-concentration tail of the halo distribution. A WDM model with particle mass 0.5 −1keV provides a better match to the observational data. However, the modified cold dark matter model, TLCDM, fits the data equally well, suggesting that the solution to the "halo cores" problem might lie in moderate changes to cosmological parameters rather than radical changes to the properties of dark matter. If CDM halos have the steeper density profiles found by Moore et al., then neither conventional LCDM nor TLCDM can reproduce the observed central densities.
Bound on the Dark Matter Density in the Solar System from Planetary Motions
High precision planet orbital data extracted from direct observation, spacecraft explorations and laser ranging techniques enable to put a strong constraint on the maximal dark matter density of a spherical halo centered around the Sun. The maximal density at Earth's location is of the order 10^5 GeV/cm^3 and shows only a mild dependence on the slope of the halo profile, taken between 0 and -2. This bound is somewhat better than that obtained from the perihelion precession limits.
The mass function of dark matter haloes
Monthly Notices of the Royal Astronomical Society, 2001
We combine data from a number of N-body simulations to predict the abundance of dark halos in Cold Dark Matter universes over more than 4 orders of magnitude in mass. A comparison of different simulations suggests that the dominant uncertainty in our results is systematic and is smaller than 10-30% at all masses, depending on the halo definition used. In particular, our "Hubble Volume" simulations of τ CDM and ΛCDM cosmologies allow the abundance of massive clusters to be predicted with uncertainties well below those expected in all currently planned observational surveys. We show that for a range of CDM cosmologies and for a suitable halo definition, the simulated mass function is almost independent of epoch, of cosmological parameters, and of initial power spectrum when expressed in appropriate variables. This universality is of exactly the kind predicted by the familiar Press-Schechter model, although this model predicts a mass function shape which differs from our numerical results, overestimating the abundance of "typical" halos and underestimating that of massive systems.
Investigating the Origins of Dark Matter Halo Density Profiles
The Astrophysical Journal, 2004
Although high-resolution N-body simulations make robust empirical predictions for the density distribution within cold dark matter halos, these studies have yielded little physical insight into the origins of the distribution. We therefore attempt to investigate the problem using analytic and semi-analytic approaches. Simple analytic considerations suggest that the inner slope of the central cusps in dark matter halos cannot be steeper than α = 2 (where ρ ∝ r −α ), with α = 1.5-1.7 being a more realistic upper limit. Moreover, our analysis suggests that any number of effects, whether real (eg. angular momentum imparted by tidal torques and secondary perturbations) or artificial (eg. two-body interactions, the accuracy of the numerical integrator, round-off errors), will result in shallower slopes. We also find that the halos should exhibit a well-defined relationship between r peri
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.