HerMES: Spectral Energy Distributions of Submillimeter Galaxies at z >4

Abstract

We present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimeter galaxies at $z>$4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimeter/millimeter photometry, we construct their Spectral Energy Distributions (SED) and a composite model to fit the SEDs. The model includes a stellar emission component at $\hat{I}{»}_{\mathrm{rest}}<$ 3.5$\hat{I}¼$m; a hot dust component peaking at $\hat{I}{»}_{rest}\sim$ 5$\hat{I}¼$m; and cold dust component which becomes significant for $\hat{I}{»}_{\mathrm{rest}}>$ 50$\hat{I}¼$m. Six objects in the sample are detected at 250 and 350$\hat{I}¼$m. The dust temperatures for the sources in this sample are in the range of 40$-$80 K, and their $L_{\mathrm{FIR}}$ $\sim$ 10${}^{13}$ L${}_{\odot }$ qualifies them as Hyper$-$Luminous Infrared Galaxies (HyperLIRGs). 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 24$\hat{I}¼$m detections corresponding to a rest-frame 4.5$\hat{I}¼$m luminosity of Log${}_{10}$(L${}_{4.5}$ / L${}_{\odot }$) = 11 $\sim$ 11.5. Their L${}_{4.5}$/$L_{\mathrm{FIR}}$ ratios are very similar to those of starburst dominated submillimeter galaxies at $z\sim$ 2. The $L_{\mathrm{CO}}-L_{\mathrm{FIR}}$ relation for this sample is consistent with that determined for local ULIRGs and SMGs at $z\sim$ 2. We conclude that submillimeter galaxies at $z>$ 4 are hotter and more luminous in the FIR, but otherwise very similar to those at $z\sim$ 2. None of these sources show any sign of the strong QSO phase being triggered.

49 pages, 15 figures. Submitted to ApJ