Morphological Statistic of Milky Way-like Galaxies

We analyze the spiral morphology of 1,738 nearby galaxies with similar Hubble type of the Milky Way (i<60, z<0.048) using multi-band optical images from the Sloan Digital Sky Survey and Digitized Sky Survey. Multiple-arm systems dominate, comprising about 50-60% of the sample and about 75% of large galaxies (d max 18 kpc). In 90 plus or minus3 % of multiple-arm galaxies, two inner arms extend into multiple outer arms; three-arm inner structures occur in 9 plus or minus2 %, and four or more are rare (<1 %). Morphology and inner-arm counts are consistent across bands at about 80%. Bifurcation points, marking the transition from two inner arms to multiple outer arms, occur in up to about 40% of galaxies, are more prominent in bluer bands tracing younger stellar populations, and cluster within 4-7 kpc of galaxy centers. These statistics suggest that the Milky Way's inner two-arm and outer multiple-arm morphology, including bifurcations at similar radii, is broadly consistent with that of a typical multiple-arm spiral galaxy.