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Pairwise velocities in the Halo Model: Luminosity and Scale Dependence | | Anze Slosar
; Uros Seljak
; Argyro Tasitsiomi
; | | Date: |
8 Jul 2005 | | Subject: | astro-ph | | Abstract: | We investigate the properties of the pairwise velocity dispersion as a function of galaxy luminosity in the context of a halo model. We derive the distribution of velocities of pairs at a given separation taking into account both one-halo and two-halo contributions. We show that pairwise velocity distribution in real space is a complicated mixture of host-satellite, satellite-satellite and two-halo pairs. The peak value is reached at around 1 Mpc/h and does not reflect the velocity dispersion of a typical halo hosting these galaxies, but is instead dominated by the satellite-satellite pairs in high mass clusters. This is true even for cross-correlations between bins separated in luminosity. As a consequence the velocity dispersion at a given separation can decrease with luminosity, even if the underlying typical halo host mass is increasing, in agreement with some recent observations. We compare our findings to numerical simulations and find a good agreement. Numerical simulations also suggest a luminosity dependent velocity bias, which depends on the subhalo mass. We develop models of the auto and cross-correlation function of luminosity subsamples of galaxies in the observable r_proj - pi space and argue that the fingers of god effects extend to large separations and depend both on velocity and density correlations. Finally, we develop a method to extract an average pair-weighted velocity dispersion, dominated by satellite-satellite pairs, from the observations and show that it can estimate it to about 10%. | | Source: | arXiv, astro-ph/0507203 | | Services: | Forum | Review | PDF | Favorites | |
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