The In-situ Origins of Dwarf Stellar Outskirts in FIRE-2
  Extended, old, and round stellar halos appear to be ubiquitous around
high-mass dwarf galaxies ($10^{8.5}<M_\star/M_\odot<10^{9.6}$) in the observed
universe. However, it is unlikely that these dwarfs have undergone a sufficient
number of minor mergers to form stellar halos that are composed of
predominantly accreted stars. Here, we demonstrate that FIRE-2 (Feedback in
Realistic Environments) cosmological zoom-in simulations are capable of
producing dwarf galaxies with realistic structure, including both a thick disk
and round stellar halo. Crucially, these stellar halos are formed in-situ,
largely via the outward migration of disk stars. However, there also exists a
large population of "non-disky" dwarfs in FIRE-2 that lack a well-defined
disk/halo and do not resemble the observed dwarf population. These non-disky
dwarfs tend to be either more gas poor or to have burstier recent star
formation histories than the disky dwarfs, suggesting that star formation
feedback may be preventing disk formation. Both classes of dwarfs underscore
the power of a galaxy's intrinsic shape -- which is a direct quantification of
the distribution of the galaxy's stellar content -- to interrogate the feedback
implementation in simulated galaxies.
