  We present the first detailed study of the spatially-resolved dust continuum
emission of simulated galaxies at 1<z<5. We run the radiative transfer code
SKIRT on a sample of submillimeter-bright galaxies drawn from the Feedback in
Realistic Environments (FIRE) project. These simulated galaxies reach Milky Way
masses by z=2. Our modelling provides predictions for the full rest-frame
far-ultraviolet-to-far-infrared spectral energy distributions of these
simulated galaxies, as well as 25-pc-resolution maps of their emission across
the wavelength spectrum. The derived morphologies are notably different in
different wavebands, with the same galaxy often appearing clumpy and extended
in the far-ultraviolet yet an ordered spiral at far-infrared wavelengths. The
observed-frame 870-$\mu$m half-light radii of our FIRE-2 galaxies are
~0.5-4kpc, consistent with existing ALMA observations of galaxies with
similarly high redshifts and stellar masses. In both simulated and observed
galaxies, the dust continuum emission is generally more compact than the cold
gas and the dust mass, but more extended than the stellar component. The most
extreme cases of compact dust emission seem to be driven by particularly
compact recent star-formation, which generates steep dust temperature
gradients. Our results confirm that the spatial extent of the dust continuum
emission is sensitive to both the dust mass and SFR distributions.

Astrophysics of Galaxies