Superbubbles vs Super-galactic winds

Here we stress some of the major dierences between supergalactic winds and giant superbubbles evolving into the giant low density haloes of galaxies. Both events are the result of massive bursts of star formation within the densest regions of the host galaxies. However, supergalactic winds are able to channel the metals produced by the recent burst straight into the intergalactic medium while superbubbles fail to reach the outskirts of the host galaxies and thus retain the newly processed metals and with them eventually raise the abundance of their ISM. We review the properties of major bursts of star formation and the critical energy (and mass of the starburst) required for mass ejection both in the case of an ISM strongly attened by rotation into a thin disk and that imposed by a more extended ISM distribution arising from a smaller rotation. The limits are thus establish for galaxies with an ISM mass in the range 10 6 M to more than 10 9 M , and are compared with a sample of local galaxies. Some of these galaxies seem to be above the critical limit despite the fact that their structure is clearly that of a superbubble. True supergalactic winds, as evidence by M82, are shown to exceed the critical limit by more than an order of magnitude and thus the limit derived by Silich & Tenorio-Tagle (2001) for mass ejection should be regarded as a lower limit.