  Deep submillimetre surveys have successfully detected distant, star-forming
galaxies, enshrouded in vast quantities of dust and which emit most of their
energy at far infrared wavelengths. These luminous galaxies are an important
constituent of the Universal star-formation history, and any complete model of
galaxy evolution must account for their existence. Although these sources have
been tentatively identified with very faint and sometimes very red optical
counterparts, their poorly constrained redshift distribution has made their
interpretation unclear. In particular, it was not understood if these galaxies
had been missed in previous surveys, or if they constituted a truly new class
of objects, undetectable at other wavelengths. By utilizing a radio selection
technique, we have isolated a sample of 20 sub-mm objects representative of the
850 micron population brighter than 5 mJy with z<~3. We show that these
galaxies are so heavily dust obscured that they remain essentially 'invisible'
to ultraviolet selection. Furthermore, relying on the radio-submillimeter flux
density ratio, we estimate their redshift distribution, finding a median of
two. While not a substitute for the thorough followup of blank field sub-mm
surveys, our results do shed light on a substantial portion of the luminous
sub-mm population with z<~3.
