The large scale inhomogeneity of the galaxy distribution

by Prof. Francesco Sylos Labini (Centro Studi e Ricerche Enrico Fermi, Roma - Istituto dei sistemi complessi (ISC) CNR, Roma - Università Cattolica, Brescia)

Tuesday 10 Jun 2008, 16:00 → 18:00 Europe/Rome

Aula Conversi (Dip. di Fisica - Edificio G. Marconi)

The Sloan Digital Sky Survey, one of the most ambitious observational programs ever undertaken in astronomy, is now completing its project measuring the position in space of about one million galaxies and thus providing a three dimensional mapping of the local universe up to a depth of several hundreds of megaparsecs. These new data allow us to address now one of most debated questions in cosmology, namely the properties and nature of galaxy large scale structures. Standard cosmological models of structure formation in the universe require that galaxy structures should have small amplitude, being homogeneous at relatively small scales. The evidences for large scale galaxy structures accumulated in the past twenty years have been absorbed in the models with the argument that structures of large spatial extension should have extremely small amplitude like the waves on the surface of the sea. This situation brings to an apparent compatibility between models and observations. In the past years we argued, on the basis of modern statistical physics concepts, that large scale structures have an intrinsically different nature from that postulated by standard models, and that they correspond to density fluctuations of large spatial extension and large amplitude characterized by scale-invariant properties. The newest data from the Sloan Digital Sky Survey project add an important and possibly definitive information on this debate. We find that large scale structures are quite typical and correspond to large amplitude in-homogeneities in the galaxy density field, making the standard interpretation untenable. We show that the standard statistical analysis is affected by systematics which are due to the inconsistent homogeneity assumption. Therefore the standard theoretical models of structure formation are in strong disagreement withe the new data. On the other hand the definitive evidence for large scale structures of large amplitude provides a novel fascinating and challenging problem in many sides which we discuss in some detail.