Detailed Astrophysical Properties of Lyman Break Galaxies

A large statistical sample of z~3 galaxies has been efficiently UV-color-selected, and confirmed spectroscopically. Here we present additional observations providing insight into the physical conditions in these Lyman Break Galaxies (LBGs), selected to be rapidly forming stars when the universe was ~15% of its current age. In Part I, we present the results of an optical/IR survey of 118 LBGs. The distribution of LBG optical/IR colors is used in conjunction with the rest-frame UV luminosity function to construct the rest-frame optical luminosity function and luminosity density of LBGs. Broad-band optical/IR spectral energy distributions are used to model the stellar populations of LBGs, and an evolutionary sequence is proposed to explain the observations. In Part II, we utilize the large database of ~1000 individual rest-frame UV LBG spectra to construct high S/N composite spectra. The composite spectra provide information about hot stars, dust, ionized gas in H II regions, and the large-scale outflows of neutral and ionized interstellar material propelled out of the galaxies by the mechanical energy injected into the interstellar medium by frequent supernova explosions. An analysis of the composite LBG spectra uncovers strong trends among the continuum and spectroscopic properties of these star-forming galaxies, and highlights the importance of outflows in determining the overall UV spectroscopic appearance. While the composite spectra reveal many properties of the galaxies, they are limited by low spectral resolution and the loss of information incurred by averaging over large samples of galaxies. Therefore, in Part III, we present some new results from a pilot program to obtain deep, higher-resolution spectroscopic observations of individual bright LBGs. With these observations, we hope to place much tighter constraints on the properties of the outflows in LBGs, and the amount of mass, energy, and metals they return to the surrounding intergalactic medium. We also present other future directions to be pursued