Herschel Detection of Dust Emission from UV-Luminous Star-Forming
  Galaxies at 3.3<z<4.3
  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 1,913
Lyman Break Galaxy (LBG) candidates is selected over an area of 5.3 deg2 in the
Bootes 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)x10^{11}L_sun
and 60-70% of their star-formation obscured by dust. The FIR SEDs peak at
lambda>100um, suggesting dust temperatures (T_d=27-30K) 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.
