Submillimetre and far-infrared spectral energy distributions of galaxies: the luminosity-temperature relation and consequences for photometric redshifts

摘要

The spectral energy distributions (SEDs) of dusty high-redshift galaxies arepoorly sampled in frequency and spatially unresolved. Their form is cruciallyimportant for estimating the large luminosities of these galaxies accurately,for providing circumstantial evidence concerning their power sources, and forestimating their redshifts in the absence of spectroscopic information. Wediscuss the suite of parameters necessary to describe their SEDs adequatelywithout introducing unnecessary complexity. We compare directly four populardescriptions, explain the key degeneracies between the parameters in each whenconfronted with data, and highlight the differences in their best-fittingvalues. Using one representative SED model, we show that fitting to even alarge number of radio, submillimetre and far-infrared (far-IR) continuumcolours provides almost no power to discriminate between the redshift and dusttemperature of an observed galaxy, unless an accurate relationship with a tightscatter exists between luminosity and temperature for the whole galaxypopulation. We review our knowledge of this luminosity-dust temperaturerelation derived from three galaxy samples, to better understand the size ofthese uncertainties. Contrary to recent claims, we stress that far-IR-basedphotometric redshifts are unlikely to be sufficiently accurate to impose usefulconstraints on models of galaxy evolution: finding spectroscopic redshifts fordistant dusty galaxies will remain essential.