Photometric Signature of Ultra-Harmonic Resonances in Barred Galaxies

TL;DR

This study uses high-resolution simulations and observational data to show that 'dark-gaps' in barred galaxies are indicators of ultra-harmonic resonances, not corotation, refining methods to identify galactic resonances.

Contribution

The paper demonstrates that 'dark-gaps' are signatures of the 4:1 ultra-harmonic resonance, challenging previous assumptions and providing a new way to identify galactic resonances.

Findings

'Dark-gaps' indicate ultra-harmonic resonances, not corotation.

Most observed barred galaxies in the sample are likely fast bars.

Kinematic measurements can indirectly infer bar corotation locations.

Abstract

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.