Photometric Signature of Ultra-Harmonic Resonances in Barred Galaxies
  Bars may induce morphological features, such as rings, through their
resonances. Previous studies suggested that the presence of 'dark-gaps', or
regions of a galaxy where the difference between the surface brightness along
the bar major axis and along the bar minor axis are maximal, can be attributed
to the location of bar corotation. Here, using GALAKOS, a high-resolution
N-body simulation of a barred galaxy, we test this photometric method's ability
to identify the bar corotation resonance. Contrary to previous work, our
results indicate that 'dark-gaps' are a clear sign of the location of the 4:1
ultra-harmonic resonance instead of bar corotation. Measurements of the bar
corotation can indirectly be inferred using kinematic information, e.g., by
measuring the shape of the rotation curve. We demonstrate our concept on a
sample of 578 face-on barred galaxies with both imaging and integral field
observations and find the sample likely consists primarily of fast bars.
