The Link between Galaxy Structure Properties and Star Formation in Local Galaxies

Abstract To investigate the role of morphology in galaxy evolution, we analyze the relationships between galaxy structure, star formation, and H i gas content. Using multiband images from the DESI Legacy Imaging Surveys, we perform detailed structural decompositions on a representative local galaxy sample from xGASS. Structural components and color properties are examined as functions of deviations from the star formation main sequence (ΔSFR MS ) and H i gas deficiency (Δ f H I ). We find that bulge fractions decrease with higher ΔSFR MS and lower stellar mass, indicating that star-forming galaxies are predominantly disk dominated while quiescent galaxies are bulge dominated. The slope of the color ( g − r ) versus ΔSFR MS relationship decreases from low to high stellar masses and from outer to inner regions, with greater color variation in massive galaxies. Color gradients are predominantly negative, becoming shallower in lower-mass galaxies and in the outer disk regions. We also identify inflection points in the color gradient and bulge fraction relations with ΔSFR MS , with main-sequence galaxies having the lowest bulge fractions and steepest color gradients. At fixed stellar mass, we observe only a slight correlation between bulge fraction and H i deficiency. However, outer disk colors show a stronger dependence on H i content than inner regions, and color gradients flatten as Δ f H I increases. These results suggest that H i gas is more closely linked to star-forming, disk-dominated systems, supporting the idea that gas accretion fuels star formation primarily in galaxy disks.