It has long been appreciated that outflows from galaxies can have a major effect on galaxy formation and evolution, influencing such basic galactic properties such as the mean metal abundance (Larson, 1974; Garnett, 2002) or even the survival of low mass galaxies (Dekel & Silk, 1986). More recent discoveries have reinvigorated interest in the role of galactic outflows, e.g.: The presence of metals in the true inter-galactic medium at low and high redshifts (Tripp et al., 2000; Songaila, 1997); that a sizable fraction of all metals ever created now reside outside galaxies (Pagel, 2002); and direct observational evidence for ubiquitous outflows from, and 100 kpc-scale cavities around, the Lyman break galaxies (Adelberger et al., 2003).
By the far the best-studied, best-understood, and arguably most common form of galactic outflow capable of polluting the IGM are superwinds (Heckman et al., 1990; Dahlem, 1997). These are loosely-collimated multi-phase outflows from actively-star forming galaxies, i.e. starburst galaxies. Within the local universe starbursts account for ~ 25% of all massive star formation (and hence metal production), and starburst activity becomes progressively more important at higher redshifts (Heckman, 1998). As all local starburst galaxies appear to have superwinds (Lehnert & Heckman, 1996), it is clear that starburst-driven winds are of major importance.
Over the last 5 years new observations of superwinds, in particular satellite-based observations in the EUV and soft and hard X-ray bands, have substantially added to our understanding of the physics behind superwinds. I will discuss how these new observations support the long-standing conceptual picture of how superwinds work, specifically (a) how superwinds are driven by the collective mechanical power of multiple supernovae (SNe) occurring within the disks (in particular the nuclei) of starburst galaxies, and (b) X-ray emission from superwinds. Where appropriate I will contrast superwinds with AGN winds (i.e. loosely collimated outflows, and not large-scale jets).