Revisiting Galactic disk and spiral arms using open clusters

Abstract

We use the largest open clusters catalogue in the post-Gaia era to provide the observational view of the Galactic disk. By compiling the physical parameters like age, distance, and kinematic information, we investigate the spatial distribution of the open clusters and revisit the spiral arms and other asymmetries in the Galactic disk. Using the young open clusters as a tracer of spiral arms, we map the spiral structure of the Galaxy and found that most of the clusters start migrating away from the spiral arms in about 10-20 Myr and fill the inter-arm regions as their age progress. Using the 3D kinematic information of 371 open star clusters, we derived different individual pattern speeds for spiral arms closely following the Milky Way rotation curve, hence favouring the transient nature of Milky Way spiral arms. The pattern rotation speeds of each spiral arm suggest that the spiral arms have not accelerated in the last 80 Myrs. Based on the distribution of open clusters younger than 700 Myr above or below the Galactic plane, we found a Solar offset of $z_\odot = 17.0\pm0.9$ pc north of the Galactic plane and estimated the scale height $z_h = 91.7 \pm 1.9$ pc from the Galactic plane.