Physics of large-scale star formation: The GAS-Dynamic aspect

The subject of the review is the nature of regions of large-scale starbursts in galaxies. Theoretical investigations are presented and discussed, for the most part. Principal attention is devoted to the gas-dynamic approach to the problem. The review has the following plan. First we give a brief summary of empirical data on superassociations as regions of collective star formation on the largest scale in disk and irregular galaxies (Sec. 2); we then describe one possible gas-dynamic scenario for the origin of these objects (Sec. 3); the key physical mechanism on which the scenario is based — a collision of shock waves — is studied on the basis of general considerations (Sec. 4), as well as using computer simulation (Sec. 5) and laboratory experiments with shock waves (Sec. 6); the possibilities for the occurrence of this process under the specific conditions of the interstellar medium in disk and irregular galaxies are discussed in Sec. 7; in Sec. 8 we then consider features of large-scale collective star formation in barred galaxies; the evolution of spiral shocks that can initiate this process is the subject of Sec. 9; possible means of generation of large-scale regions of star formation like superassociations at the center of a bar (Sec. 10) and near its ends (Sec. 11) are then described; a brief conclusion is given in Sec. 12.In memory of Victor Amazaspovich AmbartsumianTranslated from Astrofizika, Vol. 39, No. 4, pp. 627–663, October–December, 1996.