Spectroscopic Confirmation of an Extreme Starburst at Redshift 4.547

We report the spectroscopic confirmation of a submillimeter galaxy (SMG) at z = 4.547 with an estimated L IR = (0.5-2.0) × 10 13 L ☉ . The spectra, mid-IR, and X-ray properties indicate the bolometric luminosity is dominated by star formation at a rate of >1000 M ☉ yr −1 . Multiple, spatially separated components are visible in the Lyα line with an observed velocity difference of up to 380 km s −1 and the object morphology indicates a merger. The best-fit spectral energy distribution and spectral line indicators suggest the object is 2-8 Myr old and contains >10 10 M ☉ of stellar mass. This object is a likely progenitor for the massive early-type systems seen at z ∼ 2.