Portrait of the Galaxies in a Young Universe

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ABSTRACT AST 0097163Spinrad How and when do galaxies form? Studies of the microwave background radiation show that the universe was spectacularly homogeneous at redshift of approximately 1000 (corresponding to ~ 3 x 10**5 years after the Big Bang). Locally, ~ 13 Gyr later, at time 0, we find that the distribution of matter is lumpy, with baryons largely consigned to luminous, bound structures. such as galaxies and clusters of galaxies. These present-day structures can be explained by the gravitational collapse and coalescence of the overdense regions of the early Universe. A detailed understanding of this collapse, called galaxy and large-scale structure formation, stands as one of the primary challenges to astrophysicists today.This project is a, three year systematic, observational study of the earliest phases of galaxy formation. It has three scientific objectives: (1) identifying galaxies at very high redshift (z 4). (2) characterizing the galaxy population(s) at early cosmic epoch. and (3) performing detailed physical studies on a subsample of these objects as a window toward understanding the early population(s) as a whole. To conduct this study, this project will significantly augment the census of very distant (z 4) galaxies using two proven techniques: (1) photometric selection of very high-redshift protogalaxy candidates from deep ground- and space-based imaging. and (2) slit spectroscopic searches for high-redshift line emission on deep exposures. Once these high redshift objects have been found they will be studied to find the cosmic star formation history at z 5, the prevalence of dust in the early Universe, the surface density and distribution of galaxies at early, cosmic time, and the luminosity function of both photometrically -selected and line-emitting galaxies in the early Universe. In particular. how are these two populations related? Studying both populations is essential for obtaining the truest understanding of the earliest phases of galaxy evolution. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC).***