We report the Herschel SPIRE detection of dust emission arising from UV-luminous ( L \gtrsim L ^ { * } ) star-forming galaxies at 3.3 \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } z \lower 2.15 pt \hbox { $ % \buildrel < \over { \sim } $ } 4.3 .
Our sample of 1,913 Lyman Break Galaxy ( LBG ) candidates is selected over an area of 5.3 deg ^ { 2 } 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 ) \times 10 ^ { 11 } L _ { \odot } and 60 - 70 % of their star-formation obscured by dust .
The FIR SEDs peak at \lambda _ { rest } \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 100 \mu m , 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 } \equiv L _ { IR } / L _ { UV } ) is low ( \approx 3 - 4 ) compared with that observed for z \approx 2 LBGs ( { IRX _ { z \sim 2 } } \approx 7.1 \pm 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 .