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SWIFT SCIENCE

The story of our origins, begun in the crucible of the Big Bang, is largely a story of the evolution of structure and the chemical enrichment of the Universe. Beginning with the pioneering studies of galaxies in the 1920s, a host of pathfinding observations and theoretical predictions have led to the current version of this tale. At early epochs, the seeds of large structures, as fossilized in the cosmic microwave background radiation, begin to grow into the gigantic walls and voids manifest in the present-day galaxy distribution. As these initial perturbations grow, baryons accumulate in potential wells which eventually detach themselves from the universal expansion and collapse to form the first luminous stellar systems in the Universe. These fragmentary systems interact and merge to form increasingly larger systems, resulting in the galaxies that inhabit the present-day Universe. This hierarchical process of galaxy formation and evolution is a dynamic one, occurring between redshifts of 10 to 1 for the more massive systems, and at lower redshifts for the less luminous dwarfs. In this picture, the bulk of the stellar populations that comprise luminous galaxies such as the Milky Way were likely formed at redshifts beyond 1, i.e., more than 6 Gyr ago.

While this picture serves as a useful guide, many aspects are currently so poorly constrained that its applicability to the real Universe is difficult to judge. The detailed astrophysical processes that govern the formation and evolution of galaxies and determine their properties are largely unstudied: current observations provide only the crudest glimpse of the star formation, metal enrichment and dynamical merging history of the present day galaxies. In addition, the cosmological parameters that determine the geometry and expansion rate of the Universe and directly affect the formation and evolution of structure are still uncertain, as is the relationship between the initial density fluctuation spectrum and the observed large scale structure traced by luminous objects. Finally, the processes which govern star formation in a variety of environments and enrich the Universe with heavy elements, both in galaxies and in intergalactic space, remain largely in the realm of theoretical debate.

Unambiguously resolving these issues requires a highly multiplexed multi-object capability such as SWIFT. These issues can be addressed both by direct observations of millions of galaxies spread out over cosmic time, and by detailed study of the history of the Milky Way and its neighbors, as maintained in the fossil record of galactic stars. In this section, we describe a small sample of programs that SWIFT will enable astronomers to contemplate and carry out in order to address these issues. There are clearly many more.



 
next up previous contents
Next: The Growth of Structure Up: SWIFT: Spectroscopic WIde Field Previous: A SPECTROSCOPIC FACILITY FOR
Arjun Dey
1999-05-29