The Relation Between Global Gas Fraction and Outer-Disk Gravitational Anomaly in Galaxies

Based on the SPARC galaxy sample, this paper investigates the statistical rela-tionship between the global gas mass fraction (the ratio of total gas mass to totalbaryonic mass of a galaxy) and the outer-disk gravitational anomaly parameter Y(the ratio of observed rotation velocity to the velocity predicted by baryonic matter).A significant positive correlation is found: galaxies with higher gas fractions exhibitstronger gravitational anomalies in their outer disks. In galaxies with the lowestgas fractions, Y values are close to 1, consistent with Newtonian expectations; ingalaxies with the highest gas fractions, Y values can exceed 2.5. This statisticalpattern is derived entirely from observational data without any theoretical assump-tions, providing a new observational perspective for understanding galactic-scalegravitational anomalies.