Radio-mm-FIR Photometric Redshifts for (sub-)mm Galaxies

We present a comparison between the published optical, IR and CO spectroscopic redshifts of 86 (sub-)mm galaxies and their photometric redshifts as derived from long-wavelength (radio–mm–FIR) photometric data. The redshift accuracy measured for 13 sub-mm galaxies with at least one robustlydetermined colour in the radio–mm–FIR regime and additional constraining upper limits is ∆z ≈ 0.30. This accuracy degrades to ∆z ≈ 0.65 when only the 1.4GHz/850μm spectral index is used, as derived from the analysis of a subsample 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 efficiently derived for sub-mm galaxies with a precision of ∆z < 0.5 using only the rest-frame FIR to radio wavelength data, sufficient 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.