3. OBSERVED PROPERTIES OF GALACTIC WINDS

A great number of surveys have provided important statistical information on galactic winds in the local universe (e.g., Heckman, Armus, & Miley 1990; Veilleux et al. 1995; Lehnert & Heckman 1995, 1996; Gonzalez Delgado et al. 1998; Heckman et al. 2000, Rupke, Veilleux, & Sanders 2002, 2003, in prep.). Galaxy-scale winds are common among galaxies with global star formation rates per unit area _* SFR / R_opt² 0.1 M yr^-1 kpc^-2, where R_opt is the optical radius. This general rule-of-thumb also appears to apply to ultra/luminous infrared galaxies (see Section 3.3) and distant Lyman break galaxies (see Section 3.4). "Quiescent" galaxies with global star formation rates per unit area below this threshold often show signs of galactic fountaining in the forms of warm, ionized extraplanar material a few kpc above or below the galactic disks (e.g., Miller & Veilleux 2003a, 2003b and references therein). The energy input from stellar winds and supernovae in these objects elevates some of the ISM above the disk plane, but is not sufficient to produce large-scale winds.

This rule-of-thumb is conservative since a number of known wind galaxies, including our own Galaxy (Section 3.1) and several dwarf galaxies, have _* << 0.1 M yr^-1 kpc^-2 (e.g., Hunter & Gallagher 1990, 1997; Meurer et al. 1992; Marlowe et al. 1995; Kunth et al. 1998; Martin 1998, 1999; see Kunth's and Martin's contributions at this conference). The production of detectable winds probably depends not only on the characteristics of the starburst (global and local _*, starburst age), but also on the detailed properties of the ISM in the host galaxies (e.g., see the theoretical blowout criterion of MacLow & McCray 1988).

The winds in actively star-forming galaxies in the local universe show a very broad range of properties, with opening angles of ~ 0.1 - 0.5 × (4 sr), radii ranging from < 1 kpc to several 10s of kpc, outflow velocities of a few 10s of km s^-1 to more than 1000 km s^-1 (with clear evidence for a positive correlation with the temperature of the gas phase), total (kinetic and thermal) outflow energies of ~ 10⁵³ - 10⁵⁷ ergs or 5 - 20% of the total mechanical energy returned to the ISM by the starburst, and mass outflow rates ranging from < 1 M yr^-1 to > 100 M and scaling roughly with the star formation rates (see Section 3.3 below).

In the remainder of this section, we discuss a few well-studied cases of galactic winds in the local universe and summarize the evidence for winds in luminous and ultraluminous infrared galaxies at low and moderate redshifts as well as in distant Lyman break galaxies.