Forming circumnuclear disks and rings in galactic nuclei: a competition between supermassive black hole and nuclear star cluster

TL;DR

This study uses hydrodynamics simulations to explore how the interplay between supermassive black holes and nuclear star clusters influences the formation of circumnuclear disks and rings in galactic centers, matching observed structures.

Contribution

It demonstrates that the relative mass of SMBHs and NSCs determines whether extended disks or compact rings form in galactic nuclei, providing insight into observed galactic structures.

Findings

Extended disks form inside SMBH's sphere of influence.

Compact rings form outside SMBH's sphere of influence.

Results align with properties of the Milky Way's circumnuclear ring.

Abstract

We investigate the formation of circumnuclear gas structures from the tidal disruption of molecular clouds in galactic nuclei, by means of smoothed particle hydrodynamics simulations. We model galactic nuclei as composed of a supermassive black hole (SMBH) and a nuclear star cluster (NSC) and consider different mass ratios between the two components. We find that the relative masses of the SMBH and the NSC have a deep impact on the morphology of the circumnuclear gas. Extended disks form only inside the sphere of influence of the SMBH. In contrast, compact rings naturally form outside the SMBH's sphere of influence, where the gravity is dominated by the NSC. This result is in agreement with the properties of the Milky Way's circumnuclear ring, which orbits outside the SMBH sphere of influence. Our results indicate that compact circumnuclear rings can naturally form outside the SMBH sphere of influence.