The quasi-linear nearby Universe

The local Universe provides a unique opportunity for testing cosmology and theories of structure formation. As the velocities of galaxies respond to the distribution of matter-both visible and dark-the velocity field provides structural information. Here, we present an original method for the reconstruction of the quasi-linear matter density and velocity fields from galaxy peculiar velocities and apply it to the Cosmicflows-2 database of velocites. The method consists of constructing an ensemble of cosmological simulations, constrained by the standard cosmological model and the observational data. The quasi-linear density field is the geometric mean and variance of the fully nonlinear density fields of the simulations. The main nearby clusters (Virgo, Centaurus and Coma), superclusters (Shapley and Perseus-Pisces) and voids (Dipole Repeller) are robustly reconstructed. Galaxies are born 'biased' with respect to the underlying dark matter distribution. Using our quasi-linear framework, we demonstrate that the luminosity-weighted density field derived from the 2M++ redshift compilations is nonlinearly biased with respect to the matter density field. The bias diminishes in the linear regime.