Halo Shapes, Dynamics and Environment

Details Halo Shapes, Dynamics and Environment Halo Shapes, Dynamics and Environment

2006-04-07

arxiv.org/abs/astro-ph/0604155v1

Astronomy and Astrophysics

Astrophysics

To be published in "Groups Of Galaxies In The Nearby Universe", held in Chile, December 2005, edited by I.Saviane, V.Ivanov an

Scientific paper

In the hierarchical structure formation model cosmic halos are supposed to form by accretion of smaller units along anisotropic direction, defined by large-scale filamentary structures. After the epoch of primary mass aggregation (which depend on the cosmological model), violent relaxation processes will tend to alter the halo phase-space configuration producing quasi-spherical halos with a relatively smooth density profiles. Here we attempt to investigate the relation between halos shapes, their environment and their dynamical state. To this end we have run a large ($L=500 h^{-1}$ Mpc, $N_{p}=512^3$ particles) N-body simulation of a flat low-density cold dark matter model with a matter density $\Omega_{\rm m}=1-\Omega_{\Lambda}=0.3$, Hubble constant $H_{\circ}=70$ km s$^{-1}$ Mpc$^{-1}$ and a normalization parameter of $\sigma_{8}=0.9$. The particle mass is $m_{\rm p}\ge 7.7\times 10^{10} h^{-1} M_{\odot}$ comparable to the mass of one single galaxy. The halos are defined using a friends-of-friend algorithm with a linking length given by $l=0.17\bar{\nu}$ where $\bar{\nu}$ is the mean density. This linking length corresponds to an overdensity $\rho/\rho_{\rm mean}\simeq 200$ at the present epoch ($z=0$) and the total number of halos with more than 130 particles ($M>3 \times 10^{13} h^{-1} M_{\odot}$) is 57524.

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