HerMES: spectral energy distributions of submillimeter galaxies at z > 4.

We present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimetre galaxies (SMGs) at z > 4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimetre / millimeter photometry, we construct their spectral energy distributions (SEDs) and a composite model to fit the SEDs. The model includes a stellar emission component at ? rest <3.5µm, a hot dust component peaking at ? rest ~ 5µm, and cold dust component which becomes significant for ? rest > 50µm. Six objects in the sample are detected at 250 and 350µm. The dust temperatures for the sources in this sample are in the range of 40–80 K, and their L FIR ~ 10 13 Lo qualifies them as hyper-luminous infrared galaxies. The mean FIR-radio index for this sample is around (q) = 2.2 indicating no radio excess in their radio emission. Most sources in the sample have 24µmdetections corresponding to a rest-frame 4.5µm luminosity of Log 10 (L 4.5 /L ? )=11 ~ 11.5. Their L 4.5 /L FIR ratios are very similar to those of starburst-dominated SMGs at z ~ 2. The L CO - L FIR relation for this sample is consistent with that determined for local ULIRGs and SMGs at z ~ 2. We conclude that SMGs at z > 4 are hotter and more luminous in the FIR but otherwise very similar to those at z ~ 2. None of these sources show any sign of the strong QSO phase being triggered.