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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 that along the bar minor axis is 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 ultraharmonic 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 that the sample likely consists primarily of fast bars. [ABSTRACT FROM AUTHOR]

Gas interior to the bar of the Milky Way has recently been shown to be the closest example of a low-ionization (nuclear) emission region (LI(N)ER) in the universe. To better understand the nature of this gas, a sample of face-on galaxies with integral field spectroscopy is used to study the ionized gas conditions of 240 barred and 250 nonbarred galaxies, focusing on those that are most similar to the Milky Way. Strong optical line emission of [N ii ] λ6584, Hα, [O iii ] λ5007, and Hβ are used to diagnose the dominant ionization mechanisms of gas across galaxies and the Galaxy via Baldwin–Phillips–Terlevich diagrams. Barred galaxies show a strong suppression of star formation and an increase in composite and LI(N)ER-like spectra in their inner regions when compared with similar nonbarred counterparts. This effect is lessened in galaxies of very low () or very high () total stellar mass. Bar masks from Galaxy Zoo:3D show the bar's nonaxisymmetric effect on the ionized gas and help predict the face-on distribution of ionized gas conditions near the bar of the Milky Way. [ABSTRACT FROM AUTHOR]