Observations of supershells in the interstellar medium of nearby galaxies

Abstract

HI observations at sufficiently high spatial and velocity resolution have revealed a wealth of structures such as shells and bubbles in the ISM of latetype galaxies. These structures are filled with metalenriched, coronal gas from SNe which, through overpressure, powers their expansion. Material swept up by these expanding shells can go critical and form subsequent (secondary or propagating) star formation. Shells that grow larger than the thickness of the gas layer will blow out of the disk, spilling enriched material into the halo (or in the case of violent starbursts, the Intergalactic Medium). We review what has been achieved to date and present some first results of a major project based on THINGS (The HI Nearby Galaxy Survey), which aims to extend studies of the ISM in galaxies to 34 nearby systems (<10 Mpc), all observed to the same exacting standards (resolution 6 5 km s1, or better; typical detection threshold of ~5 1019 atom cm2).