# IDM2010

26-30 July 2010
Montpellier 2 University
Europe/Paris timezone

## The distribution of dark matter around galaxies : Mean surface density profile and outer structure

29 Jul 2010, 11:45
20m
Amphithéatre Dumontet (Montpellier 2 University)

### Amphithéatre Dumontet

#### Montpellier 2 University

Place Eugene Bataillon, 34095 Montpellier Cedex 5 FRANCE
Talk Structure Formation & N-body simulations

### Speaker

Mr Shogo Masaki (Nagoya University)

### Description

We study the matter distribution in and around dark halos in the standard $\Lambda$ cold dark matter ($\Lambda$CDM) universe. We use the outputs of high resolution $N$-body simulations to compute the mean surface density profile around galactic size dark matter halos. The result is compared with the observed surface density profile from the lensing magnification measurement of quasars in Sloan Digital Sky Survey (SDSS) recently reported by Menard et al. (2010). We show that the $\Lambda$CDM simulations reproduce the observed surface density profile remarkably well over a wide range of radial distance of $10 - 10^{4} h^{-1}$kpc. The mean surface density profile at small separation lengths is consistent with the theoretical prediction that dark halos have a universal Navarro-Frenk-White density profile. The observed single power-law of $\Sigma \propto R^{-0.8}$ over the distance range is explained by a simple analytic model based on a halo approach. %The time evolution of the mean surface density profile is studied to make predictions for future observations. We also study the distribution of dark matter in the outer part of the halos by measuring the mass enclosed within $\alpha R_{\rm virial}$, as a function of $\alpha$. Our simulations suggest that more than a half of total matter is contained in about 10\% volume associated with galactic halos. Assuming the SDSS galaxies are hosted by dark halos with mass $2\times 10^{12} - 10^{14}M_{\odot}$, the total mass around the halos amounts to 30 percent of the total mass in the local universe.

### Primary author

Mr Shogo Masaki (Nagoya University)

### Co-authors

Prof. Masataka Fukugita (IPMU, University of Tokyo) Prof. Naoki Yoshida (IPMU, University of Tokyo)

 Slides