3.4. Lyman Break Galaxies

Evidence for galactic winds has now been found in a number of z ~ 3 - 5 galaxies, including an important fraction of Lyman break galaxies (LBGs; e.g., Franx et al. 1997; Pettini et al. 2000, 2002; Frye, Broadhurst, & Benitez 2002; Dawson et al. 2002; Ajiki et al. 2002; Adelberger et al. 2003; Shapley et al. 2003). The best studied wind at high redshift is that of the gravitationally lensed LBG MS 1512-cB58 (Pettini et al. 2000, 2002). An outflow velocity of ~ 255 km s^-1 is derived in this object, based on the positions of the low-ionization absorption lines relative to the rest-frame optical emission lines (Ly is to be avoided for this purpose since resonant scattering and selective dust absorption of the Ly photons may severely distort the profile of this line; e.g., Tenorio-Tagle et al. 1999). The mass-conserving free wind model of Rupke et al. (2002) applied to MS 1512-cB58 (for consistency) results in a mass outflow rate of ~ 20 M yr^-1, equivalent to about 50% the star formation rate of this galaxy based on the dust-corrected UV continuum level. Similar outflow velocities are derived in other LBGs (Pettini et al. 2001). The possibly strong impact of these LBG winds on the environment at high z is discussed in the next section (Section 4.2).