Published online by Cambridge University Press: 10 November 2010
Central gaseous disks around the nuclei of flat galaxies continually increase their mass due to spiralling giant molecular clouds (GMCs) under the action of dynamical friction. The radius of the disk depends on a tidal condition in the central parts of a galaxy equal to GMC tidal disruption distance. A central part of the disk can become molecular and be able to undergo a subsequent spontaneous burst of star formation when the mean surface density of the disk becomes larger than the critical UV-opacity column density. In the outer parts of the disk, formation of gaseous clumps and stellar aggregates can be self-consistent with a characteristic clump mass of 107M⊙ and new-born stellar masses of 106M⊙ in each clump. This scenario is a good approximation to the observable characteristics of central molecular disks of normal galaxies like ours. However, the interaction of galaxies must modify the maximum cloud and stellar aggregate mass up to ∼ 108M⊙ and lead to stimulated bursts of star formation.
Bursts of star formation are frequently observed in the nuclear regions of galaxies. Observations have revealed compact nuclei surrounded by an extended disk, or disk-like HII regions with radii of about 200–500 pc (Wilson et al. 1991). These regions are, as a rule, the brightest HII regions in such galaxies. One of the main reasons for such intense starbursts is the high star formation efficiency (SFE) in galactic nuclear regions (Planesas et al. 1989).