ON THE FORMATION OF COMPACT ELLIPTICALS

A model for the formation of compact elliptical galaxies as satellites of massive galaxies is presented. It is assumed that compact elliptic als formed through a starburst and the subsequent violent collapse of the stellar system. Numerical N-body experiments show that one can und erstand the peculiar structure of compacts if they were produced as a result of the relaxation of initially cold stellar systems which were disturbed by the tidal field of a bright galaxy. The observed differen ces between compact ellipticals and low-mass giant ellipticals might t herefore result from the fact that the compacts formed within the pote ntial well of another galaxy whereas the giant ellipticals evolved as isolated systems. Constraints on the internal rotation and on the orie ntation of the major and minor axes with respect to the orbital plane of the compacts are derived. These results can be used to deproject th e observed surface brightness and velocity profiles of compact ellipti cals, and to calculate their orbital parameters. Additional N-body exp eriments of collapsing, initially clumpy protogalaxies indicate that c ompact ellipticals might be the remnants of those clumps that did not merge, but gained energy and angular momentum and formed separate sate llite systems. Thus the compacts might provide important information o n the building blocks of giant galaxies as well as on the physical con ditions of the protogalactic environment in which they evolved.