Fingers-of-God effect of infalling satellite galaxies

TL;DR

This paper develops an analytical model for the Fingers-of-God effect caused by infalling satellite galaxies, showing its significance in redshift-space distortions and implications for galaxy clustering measurements.

Contribution

It introduces a new analytical model for satellite galaxy infall velocities and demonstrates its importance in accurately modeling the FoG effect in redshift-space distortions.

Findings

Infall motion significantly affects satellite velocity distributions.

The velocity distribution becomes non-Maxwellian with dominant infall.

Ignoring infall motion leads to inaccuracies in redshift-space power spectra.

Abstract

Nonlinear redshift-space distortion known as the Fingers-of-God (FoG) effect is a major systematic uncertainty in redshift-space distortion studies conducted to test gravity models. The FoG effect has been usually attributed to the random motion of galaxies inside their clusters. When the internal galaxy motion is not well virialized, however, the coherent infalling motion toward the cluster center generates the FoG effect. Here we derive an analytical model of the satellite velocity distribution due to the infall motion combined with the random motion. We show that the velocity distribution becomes far from Maxwellian when the infalling motion is dominant. We use simulated subhalo catalogs to find that the contribution of infall motion is important to massive subhalos and that the velocity distribution has a top-hat like shape as expected from our analytic model. We also study the FoG effect due to infall motion on the redshift-space power spectrum. Using simulated mock samples of luminous red galaxies constructed from halos and massive subhalos in N-body simulations, we show that the redshift-space power spectra can differ from expectations when the infall motion is ignored.