  We have observed the dust continuum of ten z=3.1 Lyman Break Galaxies with
the Atacama Large Millimeter/Submillimeter Array at ~450 mas resolution in Band
7. We detect and resolve the 870um emission in one of the targets with an
integrated flux density of S(870)=(192+/-57) uJy, and measure a stacked 3-sigma
signal of S(870)=(67+/-23) uJy for the remaining nine. The total infrared
luminosities estimated from full spectral energy distribution fits are
L(8-1000um)=(8.4+/-2.3)x10^10 Lsun for the detection and
L(8-1000um)=(2.9+/-0.9)x10^10 Lsun for the stack. With HST ACS I-band imaging
we map the rest-frame UV emission on the same scale as the dust, effectively
resolving the 'infrared excess' (IRX=L_FIR/L_UV) in a normal galaxy at z=3.
Integrated over the galaxy we measure IRX=0.56+/-0.15, and the galaxy-averaged
UV slope is beta=-1.25+/-0.03. This puts the galaxy a factor of ~10 below the
IRX-beta relation for local starburst nuclei of Meurer et al. (1999). However,
IRX varies by more than a factor of 3 across the galaxy, and we conclude that
the complex relative morphology of the dust relative to UV emission is largely
responsible for the scatter in the IRX-beta relation at high-z. A naive
application of a Meurer-like dust correction based on the UV slope would
dramatically over-estimate the total star formation rate, and our results
support growing evidence that when integrated over the galaxy, the typical
conditions in high-z star-forming galaxies are not analogous to those in the
local starburst nuclei used to establish the Meurer relation.
