Galaxy formation revisited

The statistical properties of galaxies are used to infer the distribution of specific binding energy with surface density for a range of Hubble types. It is argued that the inferred locus characterizes physical conditions at the end of the dissipative phase of protogalactic evolution. Cosmological fluctuations in density provide the initial conditions at the onset of galaxy formation, and the critical surface density for radiative cooling to have occurred in protogalactic gas clouds provides a necessary lower bound for star formation. If gas is supported in, and eventually driven from, galactic potential wells by energy input from forming and dying stars, many of the statistical correlations found for galaxies can be understood, including those involving luminosity, effective radius, velocity dispersion or maximum rotation velocity, and metallicity. (Auth.)