Galaxies

Abstract. We present a comparison between the published optical, IR and CO spectroscopic redshifts of 86 (sub-)mm galaxies and their photometric red-shifts as derived from long-wavelength (radio{mm{FIR) photometric data. The redshift accuracy measured for 13 sub-mm galaxies with at least one robustly-determined colour in the radio{mm{FIR regime and additional constraining up-per limits is ¢z 0:30. This accuracy degrades to ¢z 0:65 when only the 1.4GHz/850m spectral index is used, as derived from the analysis of a sub-sample of 58 galaxies with robustly determined redshifts. Despite the wide range of spectral energy distributions in the local galaxies that are used in an un-biased manner as templates, this analysis demonstrates that photometric redshifts can be e±ciently derived for sub-mm galaxies with a precision of ¢z < 0:5 using only the rest-frame FIR to radio wavelength data, su±cient to guide the tuning of broad-band heterodyne observations (e.g. 100m GBT, 50m LMT, ALMA) or aid their determination in the case of a single line detection by these experiments. 1