Observations of the High Redshift Universe

Abstract

In this series of lectures, aimed for non-specialists, I review the considerable progress that has been made in the past decade in understanding how galaxies form and evolve. Complementing the presentations of my theoretical colleagues, I focus primarily on the impressive achievements of observational astronomers. A credible framework, the ΛCDM model, now exists for interpreting these observations: this is a universe with dominant dark energy whose structure grows slowly from the gravitational clumping of dark matter halos in which baryonic gas cools and forms stars. The standard model fares well in matching the detailed properties of local galaxies, and is addressing the growing body of detailed multi-wavelength data at high redshift. Both the star formation history and the assembly of stellar mass can now be empirically traced from redshifts z ≃ 6 to the present day, but how the various distant populations relate to one another and precisely how stellar assembly is regulated by feedback and environmental processes remains unclear. In the latter part of my lectures, I discuss how these studies are being extended to locate and characterize the earliest sources beyond z ≃ 6. Did early star-forming galaxies contribute significantly to the reionization process and over what period did this occur? Neither theory nor observations are well-developed in this frontier topic but the first results are exciting and provide important guidance on how we might use more powerful future facilities to fill in the details.