The nature of sub-millimeter and highly star-forming galaxies in the
  EAGLE simulation
  We exploit EAGLE, a cosmological hydrodynamical simulation, to reproduce the
selection of the observed sub-millimeter (submm) galaxy population by selecting
the model galaxies at $z \geq 1$ with mock submm fluxes $S_{850} \geq 1$ mJy.
There is a reasonable agreement between the galaxies within this sample and the
properties of the observed submm population, such as their star formation rates
(SFRs) at $z<3$, redshift distribution and many integrated galaxy properties.
We find that the bulk of the $S_{850} \geq 1$ mJy model population is at $z =
2.5$, and that they are massive galaxies ($M_* \sim 10^{11}$ Msol) with high
dust masses ($M_{\mathrm{dust}} \sim 10^{8}$ Msol), gas fractions
($f_{\mathrm{gas}} \approx 50$%) and SFRs ($\dot M_* \approx 100$ Msol/yr).
They have major and minor merger fractions similar to the general population,
suggesting that mergers are not the primary driver of the model submm galaxies.
Instead, the $S_{850} \geq 1$ mJy model galaxies yield high SFRs primarily
because they maintain a significant gas reservoir as a result of hosting an
undermassive black hole. In addition, we find that not all highly star-forming
EAGLE galaxies have submm fluxes $S_{850} > 1$ mJy. Thus, we investigate the
nature of $z \geq 1$ highly star-forming Submm-Faint galaxies (i.e., $\dot M_*
\geq 80$ Msol/yr but $S_{850}< 1$ mJy). We find they are similar to the model
submm galaxies; being gas rich and hosting undermassive black holes, however
they are typically lower mass ($M_* \sim 10^{10}$ Msol) and are at higher
redshifts ($z>4$). These typically higher-$z$ galaxies show stronger evidence
for having been triggered by major mergers, and critically, they are likely
missed by current submm surveys due to their higher dust temperatures. This
suggests a potentially even larger contribution to the SFR density at $z > 3$
from dust-obscured systems than implied by current observations.
