The Origin of Parsec-Scale Gaseous and Stellar Disks in the Galactic Center and AGNs

TL;DR

This paper proposes that parsec-scale gaseous and stellar disks near galactic centers form from the partial accretion of molecular clouds, which can lead to star formation and explain observed disk properties in the Milky Way and Seyfert galaxies.

Contribution

It introduces a cloud capture model for disk formation around black holes, linking empirical black hole-disk size relations to this process and providing insights into galactic nucleus dynamics.

Findings

Disk formation results from angular momentum cancellation during cloud capture.

The model explains the observed black hole mass and disk size scaling relation.

Galactic center disks serve as a bridge to understanding distant megamaser disks.

Abstract

The Galactic center stellar disk and the circumnuclear ring provide a unique opportunity to study in detail the dynamics and physical conditions of distant molecular disks in the nuclei of galaxies. One of the key questions is how these disks form so close to their host black holes and under what condition they form stars in a tidally stressed environment. We argue that disk formation around a massive black hole is due to partial accretion of extended molecular clouds that temporarily pass through the central region of the Galaxy. The cancellation of angular momentum of the gravitationally focused gas naturally creates a compact gaseous disk. The disk can potentially become gravitationally unstable and form stars. We apply these ideas to explain the origin of sub-parsec megamaser disks found in the nuclei of Seyfert 2 galaxies. We show that an empirical scaling relation between the mass of the black hole and the size of the disk can be understood in the context of the cloud capture scenario. We conclude that the stellar and gas disks found in our Galactic center act as a bridge to further our understanding of more distant mega-maser disks in the nuclei of Seyfert 2 galaxies.