Searching for gravitational lenses in the distant universe

FIRST has the ideal combination of sensitivity and angular resolving power to determine the bright counts of galaxies over a large area of sky in the submillimetre (submm) waveband. Important information about the evolution of galaxies at moderate redshifts will be provided by the analysis of these counts, and the effects of gravitational lensing will make the counts even more significant for observational cosmology. This paper describes the flux and surface densities of lensed galaxies in the submm waveband and explains how FIRST could be used to discover several tens of lenses. The Planck and FIRST missions are very well suited to cooperate in this programme, and together could compile a larger sample of several hundred lenses. FIRST will be able to detect the signal due to the Sunyaev-Zel'dovich (SZ) effect in a large sample of clusters. These observations could also be used to investigate submm-wave lensing by clusters, and to infer the properties of the population of faint distant galaxies.