Rest-frame ultraviolet spectra of z ∼ 3 Lyman break galaxies

We present the results of a systematic study of the rest-frame UV spectroscopic properties of Lyman break galaxies (LBGs). The database of almost 1000 LBG spectra proves useful for constructing high signal-to-noise composite spectra. The composite spectrum of the entire sample reveals a wealth of features attributable to hot stars, H II regions, dust, and out. owing neutral and ionized gas. By grouping the database according to galaxy parameters such as Lyalpha equivalent width, UV spectral slope, and interstellar kinematics, we isolate some of the major trends in LBG spectra that are least compromised by selection effects. We find that LBGs with stronger Lyalpha emission have bluer UV continua, weaker low-ionization interstellar absorption lines, smaller kinematic offsets between Lyalpha and the interstellar absorption lines, and lower star formation rates. There is a decoupling between the dependence of low- and high-ionization outflow features on other spectral properties. Additionally, galaxies with rest-frame W-Lyalpha greater than or equal to 20 Angstrom in emission have weaker than average high-ionization lines and nebular emission lines that are significantly stronger than in the sample as a whole. Most of the above trends can be explained in terms of the properties of the large-scale outflows seen in LBGs. According to this scenario, the appearance of LBG spectra is determined by a combination of the covering fraction of out. owing neutral gas, which contains dust and the range of velocities over which this gas is absorbing. In contrast, the strengths of collisionally excited nebular emission lines should not be affected by the nature of the outflow, and variations in these lines may indicate differences in the temperatures and metallicities in H II regions of galaxies with very strong Lyalpha emission. Higher sensitivity and spectral resolution observations are still required for a full understanding of the covering fraction and velocity dispersion of the out. owing neutral gas in LBGs and its relationship to the escape fraction of Lyman continuum radiation in galaxies at z similar to 3.