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 HI gas content. Using multi-band 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 ($\rm \Delta SFR_{MS}$) and HI gas deficiency ($\rm \Delta f_{HI}$). We find that bulge fractions decrease with higher $\rm \Delta SFR_{MS}$ and lower stellar mass, indicating that star-forming galaxies are predominantly disc-dominated, while quiescent galaxies are bulge-dominated. The slope of the color ($g-r$) versus $\rm \Delta SFR_{MS}$ 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 $\rm \Delta SFR_{MS}$, 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 HI deficiency. However, outer disk colors show a stronger dependence on HI content than inner regions, and color gradients flatten as $\rm \Delta f_{HI}$ increases. These results suggest that HI gas is more closely linked to star-forming, disc-dominated systems, supporting the idea that gas accretion fuels star formation primarily in galaxy disks.