A Study of the Physical Properties and Star Formation Activity of a Large Sample of Molecular Clouds. I. Distances

Abstract Accurate distances to molecular clouds are crucial for determining their physical properties, understanding star formation, and tracing Galactic spiral structure. A total of 103,517 molecular clouds have been identified by the DBSCAN algorithm in the Milky Way Imaging Scroll Painting (MWISP) Phase I CO survey ( l = 9 . ° 75–229 . ° 75, ∣ b ∣ ≤ 5 . ° 25), most of which lack reliable distances. In this work, we propose three independent methods, all of which match the molecular cloud’s velocity-integrated-intensity maps of 12 CO lines from the MWISP with the three-dimensional dust extinction maps derived from Gaia, Pan-STARRS 1, and the Two Micron All Sky Survey, to determine molecular cloud distances. We present a catalog of 1573 molecular clouds with robust distances ranging from ∼150 to ∼3000 pc, 90% of which are measured for the first time, with typical statistical and systematic uncertainties of ∼20% and ∼10%, respectively. We also derive their physical properties, such as their mass and sizes. This publicly available catalog of molecular clouds with distances provides a foundation for testing molecular cloud scaling relations and probing how cloud conditions influence star formation across diverse Galactic environments.