Physical Properties of the Lyα Forest in a Cold Dark Matter Cosmology

Abstract

We discuss the origin and physical nature of the Ly alpha forest absorption systems as found in hydrodynamical simulations of the intergalactic medium (IGM) in a standard cold dark matter cosmology ( Omega = 1, H0 = 50 km s-1 Mpc-1, sigma 8 = 0.7). The structures of the systems that give rise to the Ly alpha forest span a wide range in morphologies, depending on the density contrast. Highly overdense systems, rho b/ rho bar b>~10 , where rho b denotes baryon density, tend to be spheroidal and are located at the intersections of an interconnecting network of filaments of moderate overdensity, 1 ~ 15) correspond to the highly overdense spheroidal structures, moderate column density systems (13