Linear redshift space distortions for cosmic voids based on galaxies in redshift space

TL;DR

This paper investigates how cosmic voids in galaxy surveys trace dark matter fluctuations in redshift space, revealing that voids' redshift space distortions can be characterized by a beta factor similar to galaxies, with implications for cosmological measurements.

Contribution

It demonstrates that voids' large-scale distribution in redshift space can be modeled similarly to galaxies, and measures void beta factors consistent with galaxy beta factors in mock catalogs.

Findings

Void beta factors are consistent with galaxy beta factors in mocks.

Void beta factors need to be treated as free parameters in RSD analyses.

Void distribution traces dark matter fluctuations in redshift space.

Abstract

Cosmic voids found in galaxy surveys are defined based on the galaxy distribution in redshift space. We show that the large scale distribution of voids in redshift space traces the fluctuations in the dark matter density field \delta(k) (in Fourier space with \mu being the line of sight projected k-vector): \delta_v^s(k) = (1 + \beta_v \mu^2) b^s_v \delta(k), with a beta factor that will be in general different than the one describing the distribution of galaxies. Only in case voids could be assumed to be quasi-local transformations of the linear (Gaussian) galaxy redshift space field, one gets equal beta factors \beta_v=\beta_g=f/b_g with f being the growth rate, and b_g, b^s_v being the galaxy and void bias on large scales defined in redshift space. Indeed, in our mock void catalogs we measure void beta factors being in good agreement with the galaxy one. Further work needs to be done to confirm the level of accuracy of the beta factor equality between voids and galaxies, but in general the void beta factor needs to be considered as a free parameter for RSD studies.