Dust temperature and the submillimeter-radio flux density ratio as a redshift indicator

It is difficult to identify the distant galaxies selected in existing submillimeter (submm)-wave surveys, because their positional accuracy is only several arcseconds. Currently, centimeter-wave VLA observations are required in order to determine sub-arcsec positions, and so to make reliable optical identifications. Carilli & Yun (1999) pointed out that the ratio of the radio and submm-wave flux densities provides a redshift indicator for dusty star-forming galaxies, when compared with the tight correlation observed between the far-infrared and radio flux densities for low-redshift galaxies. This method provides a useful, albeit imprecise, indication of the distance to a submm-selected galaxy. However, because the degeneracy between the effects of increasing the redshift of a galaxy and decreasing its dust temperature is not broken, it does not provide an unequivocal redshift estimate.