Perhaps the most debated topic in galaxy formation today is the question of when and how the first galaxies formed. Some parts are well-understood: cosmological simulations of the formation of structure in the universe show that galaxies form by gravitational collapse of dark matter, in a web-like distribution of clusters, filaments and voids. However, the complex interplay of baryons and dark matter leading to the formation and evolution of star-forming galaxies is much more difficult to describe in detail. Outstanding questions include the relationship between galaxies and the large scale structures in which they form, and the identification and characterization of galaxies in the early universe.
My research addresses these questions using optical and infrared observations of galaxies and their environments. Recent surveys have begun to identify galaxies in large numbers at redshifts z~5-6, when the universe was only ~1 Gyr old, and candidate galaxies at even higher redshifts are now being found as well. The general properties of these galaxies can be estimated from their broadband spectral energy distributions: they are young and low in mass, and are also likely to have low metallicities (the fraction of elements heavier than helium, produced by stars) and little dust. Because of their distance (and hence faintness), however, detailed analysis of the spectra of these galaxies---which would give much deeper insight into their histories, contents and physical conditions---will remain impossible until the advent of future, larger ground- and space-based observatories. Until the technology is available to examine these most distant galaxies, perhaps the best way to study the physics of galaxies under such unique conditions is through careful examination of plausibly similar objects at somewhat lower redshifts, where a great deal of detailed information is available. We are conducting detailed studies of such galaxies, focusing on objects which are young and low in mass, but also both low in metallicity and with very little dust, precisely the properties predicted for galaxies in the very early universe.
In addition to studying the galaxies themselves, we can study the gas that surrounds them and their interactions with the intergalactic medium. Some of the most enigmatic objects in the distant universe are the so-called "Lyα Blobs," extended regions of emission from hydrogen gas. These are the largest luminous objects in the universe, with sizes many times larger than a galaxy, and their origin is not fully understood. They may represent cooling radiation from gas falling into galaxies, and so mark the sites of the most active formation of massive galaxies, or they may be produced by the scattering of photons produced within galaxies embedded in large clouds of outflowing gas. We have recently presented observations of large-scale structure traced by such blobs, and further observations will address their kinematics and metallicities, clarifying their relationship with galaxies.