On counter-rotating, self-gravitating warped discs in galactic nuclei

Abstract

We present the results of our simulations regarding the evolution of self-gravitating, counter-rotating warped discs surrounding supermassive black holes in galactic nuclei. We assume that first, a disc forms around a central black hole and settles into a steadily precessing warped disc configuration. Then, a counter-rotating, nearly planar disc forms around the pre-existing one. Modeling a disc as a collection of concentric, circular, tilted rings of non-negligible mass, we find a steadily precessing equilibrium warped disc solution for the inner disc for a set of parameters relevant to discs in galactic nuclei. By assuming different inclination angles between the inner and the outer discs, we follow their orbital evolution and construct their position-velocity diagrams and maps. Our results suggest that when the outer disc initially lies at the equatorial plane of the inner one, but counter-rotates, the two discs evolve without loosing their coherence. However, when the outer disc is initially inclined to the inner one, the inclinations of the rings making up the discs are altered such that the outer disc looses its coherence and becomes disrupted.