The Ly-alpha forest in a truncated hierarchical structure formation

Abstract

The Ly-alpha forest provides important constraints on the smoothness of the universe on large scales. We calculate the flux distribution along line-of-sight to quasars in a universe made of randomly distributed clumps, each of them with a Rayleigh-L`evi fractal structure. We consider the probability distribution function of the normalised flux in the line-of-sight to quasars. We show that the truncated clustering hierarchy model shows far too many voids along the line-of-sight to quasars compared with the observed flux distribution and the distribution in a Cold Dark Matter model. This supports the common view that on large scales the universe is homogeneous, rather than fractal-like.