The Dynamics of the Circumnuclear Disk and its environment in the Galactic Centre

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstraße 15, 69121 Heidelberg, Germany

Corresponding author: B. Vollmer, bvollmer@mpifr-bonn.mpg.de

Received: 27 July 2001
Accepted: 19 March 2002

Abstract

We address the question of the dynamics in the inner 50 pc of the Galactic Centre. In a first step we investigate the cloud–cloud collision rate in the Circumnuclear Disk (CND) with the help of a three dimensional N–body code using gas particles that can have inelastic collisions. The CND might be a longer lived structure than previously assumed. The whole disk–like structure of the CND can thus survive for several million years. A realistic simulation of the CND shows the observed disk height structure. In a second step the environment of the CND is taken into account. Retrograde and prograde encounters of a cloud of several 10 falling onto an already existing nuclear disk using different energy loss rates per collision are simulated. The influence of the energy loss rate per collision on the evolution of the mass accretion and cloud collision rates is strongest for a prograde encounter. A composite data cube of two different snapshots of a prograde encounter together with the CND shows striking similarity with the observed Sgr A cloud complex. The current appearance of the Galactic Centre environment can thus be explained by at least two dynamically distinct features together with the CND. The current mass accretion rate within the CND ranges between 10^-3 and 10 yr^-1. It can rise up to several 10 yr^-1 during massive accretion events.