  It is difficult to identify the distant galaxies selected in existing
submillimetre-wave surveys, because their positions are known at best to only
several arcseconds. Centimetre-wave VLA observations are required in order to
determine positions to subarcsecond accuracy, and so to allow reliable optical
identifications to be made. Carilli & Yun pointed out that the ratio of the
radio to submillimetre-wave flux densities provides a redshift indicator for
dusty star-forming galaxies, when compared with the tight correlation between
the far-infrared and radio flux densities observed in low-redshift galaxies.
This method does provide a useful, albeit imprecise, indication of the distance
to a submillimetre-selected galaxy. Unfortunately, it does not provide an
unequivocal redshift estimate, as the degeneracy between the effects of
increasing the redshift of a galaxy and decreasing its dust temperature is not
broken.
