Massive Low Surface Brightness Galaxies in the EAGLE Simulation
  We investigate the formation and properties of low surface brightness
galaxies (LSBGs) with $M_{*} > 10^{9.5} \mathrm{M_{\odot}}$ in the EAGLE
hydrodynamical cosmological simulation. Galaxy surface brightness depends on a
combination of stellar mass surface density and mass-to-light ratio ($M/L$),
such that low surface brightness is strongly correlated with both galaxy
angular momentum (low surface density) and low specific star formation rate
(high $M/L$). This drives most of the other observed correlations between
surface brightness and galaxy properties, such as the fact that most LSBGs have
low metallicity. We find that LSBGs are more isolated than high surface
brightness galaxies (HSBGs), in agreement with observations, but that this
trend is driven entirely by the fact that LSBGs are unlikely to be close-in
satellites. The majority of LSBGs are consistent with a formation scenario in
which the galaxies with the highest angular momentum are those that formed most
of their stars recently from a gas reservoir co-rotating with a high-spin dark
matter halo. However, the most extended LSBG disks in EAGLE, which are
comparable in size to observed giant LSBGs, are built up via mergers. These
galaxies are found to inhabit dark matter halos with a higher spin in their
inner regions ($<0.1r_{200c}$), even when excluding the effects of baryonic
physics by considering matching halos from a dark matter only simulation with
identical initial conditions.
