  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.
