Fractal correlations in the CfA2-South redshift survey

We report our analysis of the properties of galaxy clustering for a new redshift sample of galaxies, the CfA2-South catalog, using statistical methods which do not rely on the assumption of homogeneity. We find that, up to ~ 20 Mpc/h, which is the largest scale to which correlation properties can be reliably inferred, the galaxy clustering is scale-invariant and characterized by a fractal dimension D=1.9 \pm 0.1. Further there is no statistical evidence for homogeneity at any of the larger scales (up to ~150 Mpc/h) probed more weakly by the catalog. These results means that characteristic ``correlation lengths'' for the clustering of galaxies derived using standards methods of analysis are not meaningful. Further the results are very consistent with those obtained from many other catalogs using the methods adopted here, which show the D =2 fractal continuing to beyond 100 Mpc/h. The incompleteness of the relevant data conjectured by various authors to give rise to such behaviour is therefore proved to have no significant effect (up to 20 Mpc/h) on the measured correlations.Comment: 18 pages, latex, 1 postscript figure, also available at http://www.phys.uniroma1.it/DOCS/PIL/pil.html Accepted for publication in Astrophysical Journal Letter

Scaling in cosmic structures

The study of the properties of cosmic structures in the universe is one of the most fascinating subject of the modern cosmology research. Far from being predicted, the large scale structure of the matter distribution is a very recent discovery, which continuosly exhibits new features and issues. We have faced such topic along two directions; from one side we have studied the correlation properties of the cosmic structures, that we have found substantially different from the commonly accepted ones. From the other side, we have studied the statistical properties of the very simplified system, in the attempt to capture the essential ingredients of the formation of the observed structures.Comment: 10 pages, 3 figures. Accepted for pubblication in Fractals

Fractal Cosmology in an Open Universe

The clustering of galaxies is well characterized by fractal properties, with the presence of an eventual cross-over to homogeneity still a matter of considerable debate. In this letter we discuss the cosmological implications of a fractal distribution of matter, with a possible cross-over to homogeneity at an undetermined scale R_{homo}. Contrary to what is generally assumed, we show that, even when R_{homo} -> \infty, this possibility can be treated consistently within the framework of the expanding universe solutions of Friedmann. The fractal is a perturbation to an open cosmology in which the leading homogeneous component is the cosmic background radiation (CBR). This cosmology, inspired by the observed galaxy distributions, provides a simple explanation for the recent data which indicate the absence of deceleration in the expansion (q_o \approx 0). Correspondingly the `age problem' is also resolved. Further we show that the model can be extended back from the curvature dominated arbitrarily deep into the radiation dominated era, and we discuss qualitatively the modifications to the physics of the anisotropy of the CBR, nucleosynthesis and structure formation.Comment: 7 pages, no figures, to appear in Europhysics Letter