Star formation at high redshift as traced by near-infrared Halpha surveys

Abstract

Surveys of redshifted emission lines in the near-infrared will provide unique information on the cosmic star formation history. Near-infrared Halpha surveys will probe the cosmic star formation density and the evolution of the luminosity function of star forming galaxies out to z\sim2.5, including the important z=1.5-2.0 epoch, where according to current knowledge the cosmic star formation density peaks. Halpha and other hydrogen recombination lines (except Lyman alpha) and [O II] are all useful tracers of star formation provided the luminosity function is probed to sufficiently deep levels. However, shallow surveys or surveys of Lyman alpha or [O III] emission are not suitable for measuring or even constraining the cosmic star formation density. A first estimate of the star formation density at z\approx2.25 is derived, based on a new and sensitive large-area ESO near-infrared survey for Halpha emission at this redshift. Future observational directions, at near-infrared and longer wavelengths, for reading the cosmic star formation history are outlined.