A panoramic view of the Local Group dwarf galaxy NGC 6822
  We present a panoramic survey of the isolated Local Group dwarf irregular
galaxy NGC 6822. Our photometry reaches $\sim2-3$ magnitudes deeper than most
previous studies and spans the widest area around the dwarf compared to any
prior work. We observe no stellar over-densities in the outskirts of NGC 6822
to $V\sim 30$ mag$\,$arcsec$^{-2}$ and a projected radius of $16.5$ kpc. This
indicates that NGC 6822 has not experienced any recent interaction with a
companion galaxy, despite previous suggestions to the contrary. Similarly, we
find no evidence for any dwarf satellites of NGC 6822 to a limiting luminosity
$M_V\approx -5$. NGC 6822 contains a disk of HI gas and young stars, oriented
at $\sim 60$ degrees to an extended spheroid composed of old stellar
populations. We observe no correlation between the distribution of young stars
and spheroid members. Our imaging allows us to trace the spheroid to nearly
$11$ kpc along its major axis, commensurate with the extent of the NGC 6822
globular cluster system. We find that the spheroid becomes increasingly
flattened at larger radii, and its position angle twists by up to $40$ degrees.
We use Gaia EDR3 astrometry to measure a proper motion for NGC 6822, and then
sample its orbital parameter space. While this galaxy has spent the majority of
its life in isolation, we find that it likely passed within the virial radius
of the Milky Way $\sim3-4$ Gyr ago. This may explain the apparent flattening
and twisting observed in the outskirts of its spheroid.
