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Modelling the formation of the circumnuclear ring in the Galactic centre

Author:
Mapelli, Michela  Trani, Alessandro A.  


Journal:
ASTRONOMY & ASTROPHYSICS


Issue Date:
2016


Abstract(summary):

Several thousand solar masses of molecular, atomic, and ionized gas lie in the innermost similar to 10 pc of our Galaxy. The most relevant structure of molecular gas is the circumnuclear ring (CNR), a dense and clumpy ring surrounding the supermassive black hole (SMBH), with a radius of similar to 2 pc. We propose that the CNR formed through the tidal disruption of a molecular cloud, and we investigate this scenario by means of N-body smoothed-particle hydrodynamics simulations. We ran a grid of simulations, varying cloud mass (4 x 10(4), 1.3 x 10(5) M-circle dot), initial orbital velocity (v(in) =3D 0.2-0.5 v(esc), where v(esc) is the escape velocity from the SMBH), and impact parameter (b =3D 8, 26 pc). The disruption of the molecular cloud leads to the formation of very dense and clumpy gas rings containing most of the initial cloud mass. If the initial orbital velocity of the cloud is sufficiently low (v(in) < 0.4 v(esc), for b =3D 26 pc) or the impact parameter is sufficiently small (b less than or similar to 10 pc, for v(in) > 0.5 v(esc)), at least two rings form around the SMBH: an inner ring (with radius similar to 0.4 pc) and an outer ring (with radius similar to 2-4 pc). The inner ring forms from low-angular momentum material that engulfs the SMBH during the first periapsis passage, while the outer ring forms later, during the subsequent periapsis passages of the disrupted cloud. The inner and outer rings are misaligned by similar to 24 degrees because they form from different gas streamers, which are affected by the SMBH gravitational focusing in different ways. The outer ring matches several properties (mass, rotation velocity, temperature, clumpiness) of the CNR in our Galactic centre. We speculate that the inner ring might account for the neutral gas observed in the central cavity.


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