Redshift-Space Distortions Around Voids: A Growth-Rate Measurement from Outflowing Walls

Galaxies around a void stream outward, and in redshift space that outflow stretches the void-galaxy cross-correlation along the line of sight in a pattern that measures the growth rate of structure. This paper computes the linear outflow profile for a void of radius 35 megaparsecs per h at redshift 0.5, where the growth rate is 0.761. The mean interior contrast within the void radius is -0.220, the outflow at half the radius is 405 kilometres per second, and the outflow peaks at 0.5 void radii with 405 kilometres per second before declining into the ridge. Published void distortion analyses reach fractional errors near 6 per cent on the growth combination, while the distance-matched bouncing history adopted here shifts the growth rate by 1.2 per cent. Void distortions are therefore a competitive growth measurement in their own right and, unusually among the observables in this territory, come within a factor of a few of the size of an early-history effect, though they do not reach it. All values are computed from stated assumptions, not measured.