Revealing the Bifurcations of the Milky Way Spiral Arms Based on Hi-GAL and ATLASGAL Clumps

The spiral structure of the Milky Way remains under debate. Y. Xu et al. proposed, for the first time, a multiple-arm morphology for our Galaxy, with two spiral arms in the inner disk bifurcating outward alongside additional independent arms in the outer disk. This model aligns with the statistical properties of spiral arms seen in many extragalactic spiral galaxies and differs from the traditional standard model primarily in the presence of bifurcation points. This study aims to search for observational evidence of spiral arm bifurcations in the Milky Way and constrain its structure. Using the Herschel Infrared Galactic Plane Survey and the APEX Telescope Large Area Survey of the Galaxy clump catalogs, we first reassess the spiral arm tangent points, then analyze the statistical distributions of Galactic longitude, latitude, and velocity to identify signatures of bifurcations and constrain their potential locations. Our results suggest that the Perseus and Sagittarius arms may merge near Galactic longitude ℓ ∼ 15° in the first quadrant. Symmetrically, in the fourth quadrant, the sources are distributed along the Galactic longitude with a concentration at ℓ ∼ 333°, where the Norma and Centaurus arms are likely to converge.