Direct vs Merger Mechanism Forming Counterrotating Galaxies

Abstract

A comparison of the formation of counterrotating elliptical galaxies is made in two alternative scenarios: (a) The scenario of merging of a primary and a satellite galaxy, and (b) the direct scenario, in which counterrotating galaxies are formed directly from cosmological initial conditions. We conclude that, although both scenarios might have worked in parallel, the scenario of merging has a large number of parameters that should be well tuned to form a counterrotating galaxy in contrast to the direct scenario that is controlled by only two or three parameters. This could give more chances to the direct scenario.