Galactic Supershells

Summary

The results of 3-D numerical simulations for superbubbles expanding in a sheared and cloudy gaseous disk are presented. Assuming a disk in rotational equilibrium, the effects due to the gravitational force perpedicular to the Galactic plane, differential rotation, cloud evaporation, and radiative cooling of the gas inside the hot cavity have been included. We consider a set of different stratifications for the cloud component and discuss their influence on the final bubble properties.

Introduction

Massive stars are born in groups and their collective energy input (via UV radiation, stellar winds, and supernova explosions) causes the agglomeration of large masses of gas in cold expanding supershells (see Tenorio-Tagle & Bodenheimer 1988 and references therein). These expanding supershells are common interstellar features in our Galaxy (Heiles 1979; Lozinskaya & Sitnik 1988) and in other nearby galaxies (see Brinks 1994 and references therein). In this contribution we continue the study of expanding multi-supernova shells with 3-D numerical simulations (Palouŝ 1990; Bisnovatyi-Kogan & Silich 1991; Palouŝ 1992; Silich 1992; Silich et al. 1994a) as an attempt to understand their link with the general structure of the ISM and with the star formation process.

Equations and model parameters

The expansion of large multi-supernova shells is described using the thin layer approximation. This approximation corresponds to the late stages of supernova remnant evolution and has been applied to a wide variety of astrophysical problems with both analytical and numerical methods (Bisnovatyi-Kogan & Blinnikov 1982; Tenorio-Tagle & Palouŝ 1987; Mac Low & McCray 1988; see recent reviews by Ostriker & McKee 1988; Franco et al. 1992; Tomisaka 1993).