Cosmological Applications of Halpha Surveys

Abstract

We briefly review three main applications of Halpha surveys in cosmology, namely: (1) the diffuse Halpha emission as a tracer of the free-free foreground that contaminates the fluctuations in the cosmic microwave background radiation; (2) the Halpha emission from galaxies as a measure of the formation rate of massive stars, both at low and high redshift; and (3) the diffuse Halpha emission from ionised clouds as a constraint on the local ionising background radiation.