A Large-scale 12 CO, 13 CO, and C 18 O Molecular Cloud Survey in the Outer Galactic Plane over I = [129.°75, 140.°25] and b = [−5.°25, +5.°25]

Abstract

We present the data of an unbiased J  = 1–0 12 CO/ 13 CO/C 18 O survey of molecular clouds in the Galactic plane over l  = [129.°75, 140.°25] and b  = [−5.°25, +5.°25]. For the full 10.°5 × 10.°5 region sampled at 30″, there are 1,590,120 spectra for each isotopologue. The high sensitivity and large spatial dynamic range of the maps provide valuable insights into the structure, physical properties, and kinematics of the molecular gas. The new data successfully trace the most distant spiral arm, as well as the internal subfeatures of the nearby spiral arms. The combined data set of 12 CO, 13 CO,  and C 18 O  allows us to make a more accurate inventory of gas column density and mass for molecular gas within this Galactic interval than hitherto attempted. A statistical analysis reveals that a large fraction of the observed molecular gas is emitted from regions with low excitation conditions. As expected, a considerable amount of H 2 mass is found to be confined to the spiral arms. Moreover, we find that the C 18 O emission is exclusively seen along spiral arms at current detection limits. The physical properties of molecular gas vary considerably in different spiral arms and inter-arms. We find that the column density probability density functions and the amount of relatively denser gas (traced by 13 CO or C 18 O) appear to be closely related to the level of massive star formation activity within the molecular gas. The high-quality data also reveal that the warp and flare of the Galactic plane become obvious beyond the Perseus arm in this Galactic longitude range.