Large-scale Velocities and Primordial Non-Gaussianity

TL;DR

This paper investigates how primordial non-Gaussianity affects the velocities and clustering of density peaks like galaxies and clusters, revealing significant skewness in velocity distributions and modifications to redshift-space correlations.

Contribution

It provides a new analysis of peak velocities under non-Gaussian initial conditions and extends the Kaiser formula to include non-Gaussian bias effects on large-scale structure.

Findings

Non-Gaussianity induces a skewness of ~0.1-0.2 in velocity distributions.

Halos do not acquire a velocity bias and stream with dark matter.

Modified Kaiser formula accounts for scale-dependent bias in non-Gaussian scenarios.

Abstract

We study the peculiar velocities of density peaks in the presence of primordial non-Gaussianity. Rare, high density peaks in the initial density field can be identified with tracers such as galaxies and clusters in the evolved matter distribution. The distribution of relative velocities of peaks is derived in the large-scale limit using two different approaches based on a local biasing scheme. Both approaches agree, and show that halos still stream with the dark matter locally as well as statistically, i.e. they do not acquire a velocity bias. Nonetheless, even a moderate degree of (not necessarily local) non-Gaussianity induces a significant skewness (~ 0.1-0.2) in the relative velocity distribution, making it a potentially interesting probe of non-Gaussianity on intermediate to large scales. We also study two-point correlations in redshift-space. The well-known Kaiser formula is still a good approximation on large scales, if the Gaussian halo bias is replaced with its (scale-dependent) non-Gaussian generalization. However, there are additional terms not encompassed by this simple formula which become relevant on smaller scales (k >~ 0.01 h/Mpc). Depending on the allowed level of non-Gaussianity, these could be of relevance for future large spectroscopic surveys.