Probing the Evolution of Galaxies using Redshifted Hα Emission

In this paper we review the present status and implications of H-alpha surveys at various redshifts. With the advent of sensitive wide-format near-infrared detectors on large telescopes, deep and extensive H-alpha surveys are now feasible to redshift z~2.5. The cosmic star formation history can therefore be traced out to this redshift using H-alpha alone, avoiding complications arising from the comparison of different tracers at different redshifts. The H-alpha surveys to date confirm the rapid increase in luminosity density from z=0 out to z=1, and show that this increase flattens off at higher redshifts, remaining approximately constant out to at least z~2.2. We also discuss the prospects for determining the masses of high redshift galaxies based on emission lines. A set of high-quality H-alpha rotation curves of samples of disk galaxies at a number of different redshifts would allow a study of the evolution of the Tully-Fisher relation and address fundamental issues in disk galaxy formation. Such a program remains challenging even with present-day large telescopes.