Faint Blue Galaxies

The physical properties of the faint blue galaxy population are reviewed in the context of observational progress made via deep spectroscopic surveys and Hubble Space Telescope imaging of field galaxies at various limits, and theoretical models for the integrated star formation history of the Universe. Notwithstanding uncertainties in the properties of the local population of galaxies, convincing evidence has emerged from several independent studies for a rapid decline in the volume-averaged star formation rate of field galaxies since a redshift z~1. Together with the small angular sizes and modest mean redshift of the faintest detectable sources, these results can be understood in hierarchical models where the bulk of the star formation occurred at redshifts between z~1-2. The physical processes responsible for the subsequent demise of the faint blue galaxy population remains unclear. Considerable progress will be possible when the evolutionary trends can be monitored in the context of independent physical parameters such as the underlying galactic mass.Comment: 42 pages with 10 embedded figures available in gzipped postscript from ftp://ftp.ast.cam.ac.uk/pub/rse/annrev97.ps.gz To appear in Annual Reviews Astron. Astrophys. Vol 35, (1997

Nonequivalent ensembles and metastability

This paper reviews a number of fundamental connections that exist between nonequivalent microcanonical and canonical ensembles, the appearance of first-order phase transitions in the canonical ensemble, and thermodynamic metastable behavior.Comment: 4 pages, RevTeX, 1 figure. Contribution to the Proceedings of the 31st Workshop of the International School of Solid State Physics ``Complexity, Metastability and Nonextensivity'', held at the Ettore Majorana Foundation and Centre for Scientific Culture, Erice, Sicily, Italy, July 2004. Edited by C. Tsallis, A. Rapisarda and C. Beck. To be published by World Scientific, 200

Cosmic Dawn: Studies of the Earliest Galaxies and Their Role in Cosmic Reionization

I review recent progress and challenges in studies of the earliest galaxies, seen when the Universe was less than 1 billion years old. Can they be used as reliable tracers of the physics of cosmic reionization thereby complementing other, more direct, probes of the evolving neutrality of the intergalactic medium? Were star-forming galaxies the primary agent in the reionization process and what are the future prospects for identifying the earliest systems devoid of chemical enrichment? Ambitious future facilities are under construction for exploring galaxies and the intergalactic medium in the redshift range 6 to 20, corresponding to what we now consider the heart of the reionization era. I review what we can infer about this period from current observations and in the near-future with existing facilities, and conclude with a list of key issues where future work is required.Comment: Proceedings of the 26th Solvay Conference on Physics: "Astrophysics and Cosmology", R. Blandford and A. Sevrin, eds., World Scientifi