Spin parity of spiral galaxies. IV. Differential reddening of globular cluster systems of nearby spiral galaxies.

This article focuses on a geometric model to evaluate differential reddening effects in globular cluster (GC) systems of spiral galaxies with inclined dusty disks, applied to M 31, M 33, and NGC 253. The study confirms that the near side of a galaxy’s disk—identified by a darker, dust-dominated minor axis—is associated with increased reddening of GCs behind the disk, as demonstrated for M 31 and NGC 253 using CCD photometry, while data for M 33 were inconclusive. The model quantifies the visibility of reddening asymmetry based on disk inclination and size relative to the GC halo, supporting the use of GC color differences to determine the near side of galactic disks and to study large-scale spin distributions of spiral galaxies. Statistical analyses show significant color differences consistent with differential reddening for M 31 and NGC 253, but only marginal evidence for M 33, likely due to its lower inclination and dust content.