Stability of Gas Clouds in Galactic Nuclei: An Extended Virial Theorem

Abstract

Cold gas entering the central $1$ to $10^2$ pc of a galaxy fragments and condenses into clouds. The stability of the clouds determines whether they will be turned into stars or can be delivered to the central supermassive black hole (SMBH) to turn on an active galactic nucleus (AGN). The conventional criteria to assess the stability of these clouds, such as the Jeans criterion and Roche (or tidal) limit, are insufficient here, because they assume the dominance of self-gravity in binding a cloud, and neglect external agents, such as pressure and tidal forces, which are common in galactic nuclei. We formulate a new scheme for judging this stability. We first revisit the conventional Virial theorem, taking into account an external pressure, to identify the correct range of masses that lead to stable clouds. We then extend the theorem to include an external tidal field, crucial for the stability in the region of interest -- in dense star clusters, around SMBHs. We apply our extended Virial theorem to find the correct solutions to practical problems that until now were controversial, namely, the stability of the gas clumps in AGN tori, the circum-nuclear disk in the Galactic Center, and the central molecular zone of the Milky Way. The masses we derive for these structures are orders of magnitude smaller than the commonly-used Virial masses (equivalent to the Jeans mass). Moreover, we prove that these clumps are stable, contrary to what one would naively deduce from the Roche (tidal) limit.

Submitted. Comments welcome

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Cited by in corpus (9)

• WISDOM Project -- IX Giant Molecular Clouds in the Lenticular Galaxy NGC4429: Effects of Shear and Tidal Forces on Clouds
• Unbound Debris Streams and Remnants Resulting From the Tidal Disruptions of Stars by Supermassive Black Holes
• The Gamma-ray Afterglows of Tidal Disruption Events
• The Galactic Centre source G2 was unlikely born in any of the known massive binaries
• Exhaustion of the gas next to M31's supermassive black hole
• Modeling the Galactic center gamma-ray emission with more realistic cosmic-ray dynamics
• Do tides play a role in the determination of the pre-stellar core mass function?
• Star Formation Close to Sgr A* and Beyond the Nuclear Cluster
• Non-thermal emission from fall-back clouds in the Broad-Line Region of Active Galactic Nuclei