Galactic Superwinds Circa 2001

In this contribution I summarize our current knowledge of the nature and significance of starburst-driven galactic winds (“superwinds”). Superwinds are complex multiphase outflows of cool, warm, and hot gas, dust, and magnetized relativistic plasma. The observational manifestations of superwinds result from the hydrodynamical interaction between the primary energy-carrying wind fluid and the ambient interstellar medium. Superwinds are ubiquitous in galaxies in which the global star-formation rate per unit area exceeds roughly 10 M⊙ yr −1 kpc. This criterion is met by local starbursts and the high-z Lyman Break galaxies. Several independent datasets and techniques imply that the total mass and energy outflow rates in a superwind are comparable to the starburst’s star-formation-rate and mechanical energy injection rate, respectively. Outflow speeds in interstellar matter entrained in the wind range from ∼ 10 to 10 km/s, but the primary wind fluid itself may reach velocities as high as ∼3000 km s. The available X-ray and far-UV (FUSE) data imply that radiative losses in superwinds are not significant. Superwinds may have established the mass-metallicity relation in ellipticals and bulges, polluted the present-day inter-galactic medium to a metallicity of ∼ 10 to 30% solar, heated the inter-galactic medium, and ejected enough dust into the inter-galactic medium to have potentially observable consequences.