Active galactic nucleus activity in nearby disk galaxies: The roles of bar strength and spiral arm morphology

<jats:p>The transport of gas toward galactic centers and its connection to active galactic nucleus (AGN) activity remain key open questions in galaxy evolution. In particular, the relative roles of stellar bars and spiral arms and their possible combined influence on angular momentum redistribution and supermassive black hole fueling are not yet fully understood. We investigate the dependence of AGN activity on bar strength and spiral arm morphology in nearby spiral galaxies, with a particular emphasis on disentangling their individual and joint effects while controlling for galaxy stellar mass and color. We constructed a sample of 843 morphologically undisturbed Sa--Sd galaxies from the Mapping Nearby Galaxies at Apache Point Observatory survey in the redshift range 0.026 łeq z łeq 0.1. Bar strengths, stellar masses, colors, and AGN classes were adopted from the literature, while spiral arm classes (ACs), i.e., flocculent (FL), multi-armed (MA), and grand design (GD) systems, were visually determined for the entire sample using optical imaging together with bulge--disk decomposition residual maps. The AGN fraction increases systematically with bar strength, from 0.10^ +0.02 _ -0.02 in unbarred galaxies to 0.34^ +0.03 _ -0.03 in strongly barred systems. After controlling for stellar mass and color, a statistically significant enhancement remains detectable primarily at intermediate stellar masses (10.5 łesssim łog(M_⋆/M_⊙) łesssim 11.0), whereas no significant dependence is found at higher masses. In contrast, spiral arm morphology alone does not show a robust independent connection with AGN activity once stellar mass and color are controlled, although a weak enhancement is present in intermediate-mass GD and MA systems. When bar strength and spiral AC are considered jointly, the highest AGN fraction is observed in strongly barred GD$+MA galaxies (0.39^ +0.04 _ -0.04 )$, while the lowest AGN fractions are found in unbarred FL systems $(0.09^ +0.03 _ -0.02 )$. Our results suggest that stellar mass and color drive the primary trend in AGN activity in nearby disk galaxies, while stellar bars and spiral arms act as secondary structural drivers. The effect of spiral arm morphology is weaker and becomes most apparent when considered jointly with bars. These findings highlight the importance of simultaneously accounting for stellar mass, color, and the combined large-scale morphological structure of galaxies when investigating the triggering of nuclear activity.</jats:p>