The quasi-linear nearby Universe
Résumé
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.