Core condensation in heavy halos: a two-stage theory for galaxy formation and clustering.

A model of galaxy formation is developed in which dissipation plays a role along with purely gravitational processes. The gist of the model is that the distribution of the dominant mass component on all scales arises from purely gravitational clustering, while the observed sizes and luminosity functions of galaxies are determined by gas-dynamical dissipative processes. The model accounts for the large amount of nongaseous 'dark matter', apparently making up about 80% or more of the virial mass in clusters such as Coma and which may constitute massive halos around large galaxies. At work is a process of self-similar gravitational clustering in an expanding universe. The clustering builds up in hierarchical fashion; the smaller-scale virialized systems merge into an amorphous whole when they are incorporated in a larger bound cluster. Residual gas in the resulting potential wells cools and acquires sufficient concentration to self-gravitate, forming luminous galaxies up to a limiting size. This limit agrees adequately with the masses, luminosities, and radii of large galaxies. On certain specific assumptions, a luminosity function is derived that agrees reasonably well with observation.