Multiwavelength Observations of Dusty Star Formation at Low and High Redshift

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Abstract
If high-redshift galaxies resemble rapidly star-forming galaxies in the local universe, most of the luminosity produced by their massive stars will have been absorbed by dust and reradiated as far-infrared photons that cannot be detected with existing facilities. This paper examines what can be learned about high-redshift star formation from the small fraction of high-redshift galaxies' luminosities that is emitted at accessible wavelengths. We first consider the most basic ingredient in the analysis of high-redshift surveys: the estimation of star formation rates for detected galaxies. Standard techniques require an estimate of the bolometric luminosity produced by their massive stars. We review and quantify empirical correlations between bolometric luminosities produced by star formation and the UV, mid-IR, sub-mm, and radio luminosities of galaxies in the local universe. These correlations suggest that observations of high-redshift galaxies at any of these wavelengths should constrain their star formation rates to within ~0.2-0.3 dex. We assemble the limited evidence that high-redshift galaxies obey these locally calibrated correlations. The second part of the paper assesses whether existing surveys have found the galaxies that host the majority of star formation at high redshift even though they directly detect only a small fraction of the luminosities of individual galaxies. We describe the characteristic luminosities and dust obscurations of galaxies at z ~ 0, z ~ 1, and z ~ 3. After discussing the relationship between the high-redshift populations selected in surveys at different wavelengths, we calculate the contribution to the 850 μm background from each and argue that these known galaxy populations can together have produced the entire observed background. The available data show that a correlation between star formation rate and dust obscuration Lbol,dust/LUV exists at low and high redshift alike. The existence of this correlation plays a central role in the major conclusion of this paper: most star formation at high redshift occurred in galaxies with moderate dust obscurations 1 Lbol,dust/LUV 100 similar to those that host the majority of star formation in the local universe and to those that are detected in UV-selected surveys.