SGAS 143845.1+145407: A Big, Cool Starburst At Redshift 0.816

We present the discovery and detailed multi-wavelength study of a strongly lensed luminous infrared galaxy at z = 0.816. Unlike most known lensed galaxies discovered at optical or near-infrared wavelengths, this lensed source is red, (r - K-s)(AB) = 3.9, which the data presented here demonstrate is due to ongoing dusty star formation. The overall lensing magnification (a factor of 17) facilitates observations from the blue optical through to 500 mu m, fully capturing both the stellar photospheric emission and the re-processed thermal dust emission. We also present optical and near-IR spectroscopy. These extensive data show that this lensed galaxy is in many ways typical of IR-detected sources at z similar to 1, with both a total luminosity and size in accordance with other (albeit much less detailed) measurements for samples of galaxies observed in deep fields with the Spitzer telescope. Its far-infrared spectral energy distribution is well fit by local templates that are an order of magnitude less luminous than the lensed galaxy; local templates of comparable luminosity are too hot to fit. Its size (D similar to 7 kpc) is much larger than local luminous infrared galaxies, but in line with sizes observed for such galaxies at z similar to 1. The star formation appears uniform across this spatial scale. In this source, the luminosity of which is typical of sources that dominate the cosmic infrared background, we find that star formation is spatially extended and well organized, quite unlike the compact merger-driven starbursts that are typical for sources of this luminosity at z similar to 0.Research CorporationNational Aeronautics and Space Administration (NASA)NASA through JPL/CaltechNASA Keck PI Data AwardW. M. Keck FoundationNSFUVES Paranal Observatory Project 266.D-5655Astronom