A dynamical study of the frequency of merging galaxies

A study of the expected frequency of merging galaxies, for mergers taking place in several orbital periods, is conducted on the basis of the collisional theory of their formation, using galaxy models without halos. The results indicate that the expected frequency of such mergers is an order of magnitude below the observed value for the present epoch. The need for halos to hasten mergers is highlighted. In the light of current observational evidence and the results obtained, the formation of ellipticals by dissipative collapse followed by secular evolution by the mergers is favoured.