2012ApJ...758L..31L

We report the Herschel/SPIRE detection of dust emission arising from UV-luminous (L ≳ L*) star-forming galaxies at 3.3 ≲ z ≲ 4.3. Our sample of 1913 Lyman break galaxy (LBG) candidates is selected over an area of 5.3 deg² in the Boötes field of the NOAO Deep Wide-Field Survey. This is one of the largest samples of UV-luminous galaxies at this epoch and enables an investigation of the bright end of the galaxy luminosity function. We divide our sample into three luminosity bins and stack the Herschel/SPIRE data to measure the average spectral energy distribution (SED) of LBGs at far-infrared (FIR) wavelengths. We find that these galaxies have average IR luminosities of (3-5)x10¹¹ L_☉ and 60%-70% of their star formation obscured by dust. The FIR SEDs peak at λ_rest ≳ 100 µm suggesting dust temperatures (T_d= 27-30 K) significantly colder than that of local galaxies of comparable IR luminosities. The observed IR-to-UV luminosity ratio (IRX ≡ L_IR/L_UV) is low (~3-4) compared with that observed for z ~ 2 LBGs (IRX_ z ∼ 2_~ 7.1±1.1). The correlation between the slope of the UV continuum and IRX for galaxies in the two lower luminosity bins suggests dust properties similar to those of local starburst galaxies. However, the galaxies in the highest luminosity bin appear to deviate from the local relation, suggesting that their dust properties may differ from those of their lower-luminosity and low-redshift counterparts. We speculate that the most UV-luminous galaxies at this epoch are being observed in a short-lived and young evolutionary phase.