Authors: Kanak Saha, Alister W. Graham, Isabel Rodríguez Herranz
It has long been thought that the (X/Peanut)-shaped structures are vertically buckled bars protruding (only) above and below the plane of disk galaxies. Indeed, they are preferentially noticed in near edge-on disk galaxies. However, a small, but growing, handful of spiral galaxies are now known to display peanut-shaped structures even though their disks have a relatively face-on projection, e.g. IC 5240 - indicating that (some) `peanuts' might actually be three-dimensional, i.e. dumbbell-shaped rather than banana-shaped, and that perhaps some, if not many (X/Peanut)-shaped structures, are hidden by the light of their face-on disks and have consequently been over-looked in past observational campaigns. We have performed a suite of collisionless simulations to investigate this phenomenon. We report on three simulated galaxies displaying peanut-shaped structures when their disks are seen both face-on and edge-on. These simulations reveal how to create peanuts that are a 3D structure. Furthermore, our simulated peanut structures were accompanied by ansae and an outer ring at the end of the bar - as is also seen in real galaxies such as IC 5240. For comparison, the same set of quantitative peanut parameters used to measure real galaxies have been determined for the simulated galaxies, and compared with observed peanuts. The emergent peanut structures are a maximum at half the length of the bar. Beyond the cutoff of the X/P/bowtie structure towards the end of the bar, we discover a positive/negative feature (in the face-on disk view) in the radial profile of the m=6 Fourier component that is associated with the ansae/ring. Our simulated 3D peanut structures (more precisely, self-gravitating dubbell-shaped structure) display cylindrical rotation even in near-face-on projection. In addition, we report of a kinematic pinch in the velocity map along the bar minor axis, matching that seen in the surface density map.