Precision cosmology with voids: definition, methods, dynamics

We develop a new cosmic void finding technique based on methods of Lagrangian orbit reconstruction. We propose to define voids as the source point of repulsion of the comoving motion of galaxies in the Universe. We re-define the position and the ellipticity of voids in this Lagrangian framework. We discuss the advantage of this new void finder compared to existing Eulerian techniques. We then develop an analytical model of the ellipticity of voids based on Zel’dovich approximation. We measure in N body simulation that this model is precise at the ∼0.1% level for the mean ellipticity of voids of size greater than ∼4hMpc. We estimate that at this scale, we are able to predict the ellipticity with an accuracy of σε ∼ 0.02. Finally, we compare the distribution of void shapes in N -body simulation for two different equations of state w of the dark energy. We conclude that our method is promising as a precision probe of dark energy phenomenology.