THE RELATION BETWEEN THE VIRIAL THEOREM AND THE FUNDAMENTAL PLANE OF ELLIPTICAL GALAXIES

Theanalysisofthepropertiesofasampleofelliptical galaxies for which the kinetic energy of both random and rota- tional motions are consistently dened, shows that more than half of the so-called 'tilt' of the fundamental plane of elliptical galaxies is accounted for by the non-homology in the dynami- cal structure of the systems. We nd that the kinetic energy of random motions is proportional to 1:6 0 instead of 2 . We also conrm that some fraction of the tilt is accounted for by the ro- tation. The remaining 30% of the tilt, on the other hand, can be easily explained by stellar population effects and, possibly, by spatial non-homology. We nd that, in the present sample, there isnocorrelationbetweenmass-to-lightratioandluminosity.We are thus led to conclude that the existence of the fundamental plane can be consistently explained by the virial theorem, or, in other words, that elliptical galaxies are non-homologous viri- alized systems. The presence of the dynamical non-homology casts some doubts on the use of the FP as a distance indicator.