Hubble Space Telescope observations of giant arcs: High-resolution imaging of distant field galaxies

We present Hubble Space Telescope (HST) imaging of eight spectroscopically confirmed giant arcs, pairs, and arclets. These objects have all been studied extensively from the ground, and we demonstrate the unique advantages of HST imaging in the study of such features by a critical comparison of our data with the previous observations. In particular, we present new estimates of the core radii of two clusters (Cl 0024 + 16, A370) determined from lensed features that are identifiable in our HST images. Although our HST observations include both pre- and postrefurbishment images, the depth of the exposures guarantees that the majority of the arcs are detected with diffraction-limited resolution. A number of the objects in our sample are multiply imaged, and we illustrate the ease of identification of such features when working at high resolution. We discuss the morphological and size information on these distant field galaxies in the light of HST studies of lower redshift samples. We suggest that the dominant population of star-forming galaxies at z similar to 1 is a factor of 1.5-2 times smaller in size than the equivalent population in the local field. This implies either a considerable evolution in the sizes of star-forming galaxies within the last similar to 10 Gyr or a shift in the relative space densities of massive and dwarf star-forming systems over the same timescale.