Cooling radius vs. absorption size of galaxies

The discussion of the relationship between cooling radius in two-phase adia batic halo models and observationally established maximal radius of absorpt ion in luminous galaxies at low redshift is presented. It is of paramount i mportance that any viable model of the halo is able to reproduce empirical value of the absorption cross-section of normal galaxies and its scaling wi th luminosity. Several ways for bringing the theoretical and observational values into agreement are outlined. It is of great methodological importanc e to fully assess the difficulties any model is likely to encounter when te sting predicted extent of absorption and column density distribution agains t recently obtained low-redshift Ly alpha absorption data.