  We present the first results of our HST WFPC2 F814W snapshot imaging survey,
targeting virtually all sub-mJy decimetric radio-selected star-forming
galaxies. The radio selection at ~1 GHz is free from extinction effects and the
radio luminosities are largely unaffected by AGN contamination, making these
galaxies ideal tracers of the cosmic star formation history. A sub-sample of 4
targets is presented here, selected at 1.4 GHz from the spectroscopically
homogenous and complete samples of Benn et al. (1993) and Hopkins et al.
(1999). The redshifts are confined to a narrow range around z~0.2, to avoid
differential evolution, with a radio luminosity close to L* where the galaxies
dominate the comoving volume-averaged star formation rate. We find clearly
disturbed morphologies resembling those of ultraluminous infrared galaxies,
indicating that galaxy interactions may be the dominant mechanism for
triggering star formation at these epochs. The morphologies are also clearly
different from coeval quasars and radiogalaxies, as found in star-forming
galaxies selected at other wavelengths. This may prove challenging for models
which propose direct causal links between AGN evolution and the cosmic star
formation history at these epochs. The asymmetries are typically much larger
than seen in the CFRS at similar redshifts, optical luminosities and
Halpha-derived star formation rates, indicating the possible existence of an
obscuration-related morphological bias in such samples.
