IRAC Near-Infrared Features in the Outer Parts of S4G Galaxies
  We present a catalogue and images of visually detected features, such as
asymmetries, extensions, warps, shells, tidal tails, polar rings, and obvious
signs of mergers or interactions, in the faint outer regions (at and outside of
R_25) of nearby galaxies. This catalogue can be used in future quantitative
studies that examine galaxy evolution due to internal and external factors. We
are able to reliably detect outer region features down to a brightness level of
0.03 MJy/sr per pixel at 3.6 microns in the Spitzer Survey of Stellar Structure
in Galaxies (S4G). We also tabulate companion galaxies. We find asymmetries in
the outer isophotes in 22+/-1 per cent of the sample. The asymmetry fraction
does not correlate with galaxy classification as an interacting galaxy or
merger remnant, or with the presence of companions. We also compare the
detected features to similar features in galaxies taken from cosmological zoom
re-simulations. The simulated images have a higher fraction (33 per cent) of
outer disc asymmetries, which may be due to selection effects and an uncertain
star formation threshold in the models. The asymmetries may have either an
internal (e.g., lopsidedness due to dark halo asymmetry) or external origin.
