Gaussianity of Cosmic Velocity Fields and Linearity of the Velocity-Gravity Relation

Abstract

We present a numerical study of the relation between the cosmic peculiar velocity field and the gravitational acceleration field. We show that on mildly non-linear scales (4-10 Mpc Gaussian smoothing), the distribution of the Cartesian coordinates of each of these fields is well approximated by a Gaussian. In particular, their kurtoses and negentropies are small compared to those of the velocity divergence and density fields. We find that at these scales the relation between the velocity and gravity field follows linear theory to good accuracy. Specifically, the systematic errors in velocity-velocity comparisons due to assuming the linear model do not exceed 6% in beta. To correct for them, we test various nonlinear estimators of velocity from density. We show that a slight modification of the alpha-formula proposed by Kudlicki et al. yields an estimator which is essentially unbiased and has a small variance.

11 pages, 15 figures; matches the version accepted for publication in MNRAS

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• Phase Space dynamics of triaxial collapse: Joint density-velocity evolution
• Likelihood analysis of the Local Group acceleration revisited
• Uneven flows: On cosmic bulk flows, local observers, and gravity
• Towards the optimal window for the 2MASS dipole
• Non-linear density-velocity divergence relation from phase space dynamics
• Non-linear density-velocity dynamics in $f(R)$ gravity from spherical collapse
• Motion of the Local Group as a cosmological probe