Regular distribution of star formation regions along the spiral arms and rings of disk galaxies

Recent studies have indicated that the spatial regularity in the distribution of young stellar population along the spiral arms and rings of galaxies, which was previously thought to be uncommon, is actually a fairly common occurrence. Spatial regularity has been found in the spiral arms and rings of galaxies with different morphologies, from lenticular to extremely late-type spiral. The characteristic regularity scale is equal to 350–500 pc or a multiple of that in all the galaxies studied. Theoretical models suggest a scale of instability for the stellar-gas disk around a few kpc, which is larger than what has been observed. Recent magneto-hydrodynamic simulations, however, indicate the formation of regular chains of star formation regions in spiral arms on a scale of 500–700 pc for galaxies similar to the Milky Way. Modern high-quality surveys, like PHANGS–MUSE, provide the necessary observational data (surface densities and velocity dispersions of gas and stellar population) to directly calculate the regularity scales in galaxies, with high spatial resolution and a wide field of view, which is a promising direction for research in this field.