ABSTRACT

Theoretical studies of gas dynamics in disk galaxies are reviewed in relation to the fueling of nuclear activity. Importance of self-gravitational effects in the interstellar gas component is emphasized.

FUELING PROBLEM

Recent observations have revealed that some galaxies show an unusual level of activity near the nuclear regions. One type of activity is the enhanced star formation in the central few kpc regions around galaxy nuclei. Another is the non-thermal activity which originates from sub-parsec region, which is called active galactic nuclei (AGN). This type of activity is believed to be powered by mass accretion onto supermassive black holes located in the galactic nuclei (e.g., Begelman et al. 1984). Both types of activity require adequate source of fuel. In typical AGNs, a gas supply rate of ∼ 1 M0 yr-1 is needed to generate the radiation of the observed amount. CO line observations (e.g., Kenney 1990) have detected large accumulation of a potential fuel in the form of molecular gas in the central kpc in many starburst galaxies.

Possible candidate sources of fuel are divided into local and global ones according to their spatial distribution. The difficulties for local sources such as compact star clusters have been pointed out by several works (e.g., Shlosman et al. 1990). In this article we concentrate on global sources, especially the interstellar gas in the galactic disks. Because interstellar gas is distributed on the 10 kpc scale, one problem is how the material can be channelled into the nuclear region with a sufficiently high efficiency to maintain the observed level of activity.