The Origin of Keplerian Megamaser Disks

TL;DR

This paper explains the formation of Keplerian megamaser disks in active galactic nuclei as a result of molecular clouds passing through the galactic center, revealing a correlation between disk size and black hole mass.

Contribution

It introduces a model linking molecular cloud infall to the formation of megamaser disks, explaining their properties and relation to black hole mass.

Findings

Empirical linear correlation between disk radius and black hole mass.

Disks form from molecular clouds passing through galactic nuclei.

High cloud column densities lead to disk fragmentation and star formation.

Abstract

Several examples of thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and black hole mass and that such disks are naturally formed as molecular clouds pass through the galactic nucleus and temporarily engulf the central supermassive black hole. For initial cloud column densities below about 10^{23.5} cm^{-2} the disk is non-self gravitating, but for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic centre.