On the origins of up-bending breaks in disk galaxies

Using SPITZER 3.6$\mu$m imaging, we investigate the physical and data-driven origins of up-bending (Type III) disk breaks. We apply a robust new break-finding algorithm to 175 low-inclination disk galaxies previously identified as containing Type III breaks, classify each galaxy by its outermost re-classified (via our new algorithm) break type, and compare the local environments of each resulting subgroup. Using three different measures of the local density of galaxies, we find that galaxies with extended outer spheroids (Type IIIs) occupy the highest density environments in our sample, while those with extended down-bending (Type II) disks and symmetric outskirts occupy the lowest density environments. Among outermost breaks, the most common origin of Type III breaks in our sample is methodological; the use of elliptical apertures to measure the radial profiles of asymmetric galaxies usually results in features akin to Type III breaks.