Maximum-entropy models of galaxies

Photometric and kinematic observations of elliptical galaxies are not sufficient to determine the complete phase-space distribution function of the galaxy. In general, many possible distribution functions are consistent with the available observations; statistical mechanics and information theory suggest that the most natural of these are the ones with the largest entropy. We show how to construct the maximum-entropy distribution function consistent with given emissivity and potential distributions and a given set of kinematic observations. As examples, we construct the maximum-entropy models consistent with two common spherical luminosity distributions: the Plummer model and the de Vaucouleurs R^1/4^ model. Maximum-entropy models offer a flexible and straightforward approach to modeling galaxies from limited observational data.