Gas Dynamics in the Galactic Centre: Gravity vs. Magnetism

Extract

This contribution is a summary of an impromptu and extremely interesting discussion on the nature of the forces acting on gas in the galactic centre. The origins of the gas motions in the central few parsecs are crucial for clarifying many important problems about galactic nuclei. Some of the many gas dynamics issues that were raised include: 1. are there explosive events in the galactic centre which produce outward moving gas clouds (see Heyvaerts, these proceedings)? 2. are the streamers of gas due to the tidal disruption of molecular clouds that stray in too deep in the galactic centre's tidal field (see Serabyn, these proceedings)? 3. is there circular gas motion which would be important in constraining the nature of the mass distribution inside scales of a few pc (see review by Townes, these proceedings)?

The discussion centered on gas dynamics in the molecular torus and ionized gas streamers on the 2–5 pc scale. Because reliable measurements of the magnetic field strength in the galactic centre are not yet available, several of the key points of contention will not be finally settled until the data are in. Be this as it may, the discussion boiled down to the issue of whether gravity or magnetic fields were responsible for the structures and morphology on this scale. Accordingly I will label the arguments of the two relevant camps by G (for gravitational fields as the predominant shaper of things) and M (for magnetic fields as the important agents).