HST Observations of Giant Arcs

We discuss HST imaging of eight spectroscopically-confirmed giant arcs, pairs and arclets. Although our HST observations include both pre- and post-refurbishment images, the depth of the exposures guarantees that the majority of the arcs are detected with diffraction-limited resolution. We present the 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 ∼ 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 ∼10 Gyrs or a shift in the relative space densities of massive and dwarf star-forming systems over the same time scale.