Absorption Lines from Cold Gas in Extragalactic Superbubbles

Abstract

Today, there is considerable interest in studying Superbubbles. These gigantic bubbles are blown in galaxies by the action of very powerful phenomena (e.g. stellar winds and multiple supernovae explosions (SNE) in stellar associations, collisions of clouds with galactic disks). They represent the largest space laboratory to study the physics of a dynamic multiphase interstellar medium (ISM). As a hydrodynamical consequence of the star forming processes via interaction with the surrounding gaseous medium, superbubbles may have occupied a significant volume fraction in the ISM of galaxies at the time they formed their first stars, and during their evolution in conjunction with starburst episodes. In the present day universe, well known examples are the Galactic H I supershells, the supershells of the Large and Small Magellanic Clouds (LMC & SMC), those in nearby galaxies GR 8, M101, NGC 4449, M82 identified either in H I (radio emission) and/or by their bright optical line emission (Hα). In the case of M 82, a powerful superwind emitted from the nuclear region is responsible for the observed superbubble.