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Register a new userDensity profiles and clustering of dark halos and clusters of galaxies
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Authors
Yasushi Suto
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Density profiles of cosmological virialized systems, or dark halos, have recently attracted much attention. I first present a brief historical review of numerical simulations to quantify the halo density profiles. Then I describe the latest results on the universal density profile and their observational confrontation. Finally I discuss a clustering model of those halos with particular emphasis on the cosmological light-cone effect.
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We use the statistics of strong gravitational lenses to investigate whether mass profiles with a flat density core are supported. The probability for lensing by halos modeled by a nonsingular truncated isothermal sphere (NTIS) with image separations greater than a certain value (ranging from zero to ten arcseconds) is calculated. NTIS is an analytical model for the postcollapse equilibrium structure of virialized objects derived by Shapiro, Iliev & Raga. This profile has a soft core and matches quite well with the mass profiles of dark matter-dominated dwarf galaxies deduced from their observed rotation curves. It also agrees well with the NFW (Navarro-Frenk-White) profile at all radii outside of a few NTIS core radii. Unfortunately, comparing the results with those for singular lensing halos (NFW and SIS+NFW) and strong lensing observations, the probabilities for lensing by NTIS halos are far too low. As this result is valid for any other nonsingular density profiles (with a large core radius), we conclude that nonsingular density profiles (with a large core radius) for CDM halos are ruled out by statistics of strong gravitational lenses.
We describe the first results from two observational projects aimed at measuring the amount and spatial distribution of dark matter in distant early-type galaxies (E/S0s) and clusters of galaxies. At the galaxy scale, the Lenses Structure and Dynamics (LSD) Survey is gathering kinematic data for distant (up to $zsim1$) E/S0s that are gravitational lenses. A joint lensing and dynamical analysis constrains the fraction of dark matter within the Einstein radius, the mass-to-light ratio of the stellar component, and the total slope of the mass density profile. These properties and their evolution with redshift are briefly discussed in terms of the formation and evolution of E/S0 galaxies and measurement of the Hubble Constant from gravitational time delay systems. At the cluster scale -- after careful removal of the stellar component with a joint lensing and dynamical analysis -- systems with giant radial arcs can be used to measure precisely the inner slope of the dark matter halo. An HST search for radial arcs and the analysis of a first sample are briefly discussed in terms of the universal dark matter halos predicted by CDM simulations.
The multicomponent dark matter model with self-scattering and inter-
We have determined the mass profiles of dark halos in 83 objects observed by ASCA. The point spread function of X-ray telescope was deconvoled by the Richardson-Lucy algorithm and the temperature profiles were calculated to obtain the mass profiles. The derived mass profiles are consistent with the NFW model in 0.01-1.0 r_virial. We found a good correlation between the scale radius r_s and the characteristic mass density delta_c, which indicates the self-similarity of dark halos. The spectrum index of primordial density fluctuation, P(k) propto k^n, was determined from the slope of r_s - delta_c relation. For M_200=10^12-10^15 M_solar, our analysis gives n=-1.2 +/- 0.3 with a confidence level of 90%. The mass density of dark halos is a good indicator of the mean mass density of the universe at the time when the halos were assembled, z=z_f. Assuming delta_c propto (1+z_f)^3, we have determined the epoch when each dark halo was assembled. Our analysis indicates that the field elliptical galaxies and groups of galaxies formed approximately at 1+z_f ~ 15 and at 1+z_f ~ 7-10 respectively.
We use N-body simulations to investigate the radial dependence of the density and velocity dispersion in cold dark matter (CDM) halos. In particular, we explore how closely Q rho/sigma^3, a surrogate measure of the phase-space density, follows a power-law in radius. Our study extends earlier work by considering, in addition to spherically-averaged profiles, local Q-estimates for individual particles, Q_i; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q_i(r); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q^s. The resulting Q_i^s(r) profiles follow closely a power law near the center, but show a clear upturn from this trend near the virial radius, r_{200}. The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschingers spherical secondary-infall similarity solution. In this model, Q propto r^{-1.875} in the inner, virialized regions, but departures from a power-law occur near r_{200} because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of $Q$ profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM halos beyond their characteristic scale radius.
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