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The velocity profile of galaxies around voids is a key ingredient forredshift space distortion (RSD) measurements made using the void-galaxycorrelation function. In this paper we use simulations to test whether thevelocity profile of the tracers used to find the voids matches the velocityprofile of the dark matter around these voids. A mismatch is expected and foundin the inner part of voids, where tracers are very sparse. We discuss how thisdifference is caused by a selection effect where the void centre positions arecorrelated to the particular realization of the sparse tracers and theirspatial distribution. In turn, this then affects the RSD void-galaxycorrelation analysis. We show this by evaluating the Jacobian of the real toredshift space mapping using the tracer or matter velocity profile. Differencesof the order of 20\% in the velocity profile translate into differences of theorder of few percent in the Jacobian. This small discrepancy propagates to themonopole and quadrupole of the void-tracer correlation function, producingmodifications of comparable magnitude to those from changes in $f\sigma_8$ atthe level of the statistical uncertainties from current analyses.

Velocity profiles of matter and biased tracers around voids