  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.
