Large-Scale Motions in the ISM of Elliptical and Spiral Galaxies

Summary

Large-scale non-ordered motion is produced in spiral and elliptical galaxies through various stellar events, which have been the subject of our studies. In elliptical galaxies, we have investigated the way in which stellar mass loss interacts with the hot ambient X – ray emitting interstellar gas. During this mass loss stage, stars are moving at typically 300–500 km/sec, so a bow shock develops at the front of the star and the shocked stellar mass loss is pushed backward as a slowly moving wake that extends 10^1.5pc from the star. Kelvin-Helmholtz instabilities grow in the wake, causing material to be drawn out and subsequently shocked; this is the primary heating mechanism in the stellar ejecta.

For spiral galaxies, we investigate the global nature of galactic disk gas on a scale of kiloparsecs, where star formation, mass loss, supernova heating, and radiative cooling occur. For models most appropriate to the Solar vicinity, the outflow of hot gas occurs through large connected superbubble regions of typical width 0.5 – 1 kpc. The return downward flow is organized in regions of comparable size, leading to the appearance of a convective fountain flow.

Introduction

Most of the talks at this meeting have focused on the nature of turbulence on scales where the eddies are fully developed, which conventionally means sizes less than the outer scale, typically in the range of 10⁻² − 10 pc (see Cordes, this meeting).