Lensed galaxies in Abell 370. II. The ultraviolet properties of arclets and the star formation rate at high redshift

We discuss the statistical properties of faint background galaxies detected in a deep Hubble Space Telescope ultraviolet (F336W) Wide Field Planetary Camera 2 image of the lensing cluster Abell 370 (z=0.37). By combining modelled field galaxy counts at this wavelength with a detailed mass model for the cluster, we develop techniques for predicting the expected redshift distribution of lensed sources and find the bulk of the sources should be moderately magnified sources whose redshifts lie between 0.5 and 2. We compare these predictions with redshift estimates derived from the lens inversion method which utilises the shapes of individual arclets in the context of a known field ellipticity distribution. This allows us to infer the comoving star formation rate for the range 0.5<z<2 where there is currently little spectroscopic data. We discuss our results in the context of contemporary pictures for the history of star formation. Based on observations with the NASA/ESA Hubble Space Telescope obtained from the data archive at the Space Telescope Science Institute, USA