Cosmological velocity bias
Citations Over TimeTop 10% of 1990 papers
Abstract
Gravitationally bound objects, such as galaxies, that collapse from a cosmological background can exhibit both a correlation bias and, as shown here, a significant bias in their peculiar velocity dispersion with respect to the density field. The correlation bias, bxi_, begins as a statistical enhancement that dwindles as relatively less overdense regions collapse. Ultimately, merging can diminish the correlation to less than that in the density field. Pairwise center-of-mass peculiar velocities of collapsed regions are reduced below that of the density field to a small extent by the removal of their internal velocity dispersion and by the tendency of galaxies to form preferentially near the bottom of group and cluster potential wells. More importantly, dynamical friction slows the objects and their associated halos as dynamical ciustering develops, leading to a signiflcant velocity dispersion bias, b_v_, with respect to the density field. The detailed simulations of a cold dark matter cosmology reported bere indicate that together these two kinds of bias can reconcile a galaxy correlation length of 5h^-1^ Mpc and a peculiar velocity dispersion of approximately 300 km s^-1^ with an {OMEGA} = 1 cosmology, for a range of correlation biases. Values of bxi_ ~ 1 and b_v_ ~ 0.5 are favored using additional normalizing data. For the adopted star formation algorithm, the galaxies in the simulation are found to have properties similar to those of the dense cores of dark halos.
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