The molecular clouds in a section of the third Galactic quadrant: cloud catalog

The Milky Way Imaging Scroll Painting (MWISP) is an ongoing unbiased Galactic panel CO survey, which is performed using the 13.7m telescope of PMO and observes 12CO, 13CO, and C18O (J=1-0) lines simultaneously. The detailed introductions for the telescope, the multi-beam receiver system, the observation mode, and data reduction procedures are described in Su et al. (2019). The data is 250 square degrees data (195° < l < 220°, |b| < 5 °) of 12CO, 13CO, and C18O in the third Galactic quadrant. The half-power beam width (HPBW) for the telescope at 115 GHz is about 50 arcsec. The velocity separation is about 0.16 km s-1 for 12CO and 0.17 km s-1 for 13CO and C18O lines.We provide 250 square degrees (195° < l < 220°, |b| < 5 °) of molecular cloud data. We construct three molecular cloud catalogs containing information of 12CO, 13CO, and C18O, respectively, from the position-position-velocity (PPV) datacubes. The 12CO cloud catalog contains 7069 samples identified based on the DBSCAN algorithm. We develop a new algorithm, the stacking bump algorithm, for identifying 13CO and C18O emission by searching for weak signals in the original spectra of 13CO and C18O within the boundary in PPV space defined by the 12CO cloud. At above the 2 σ threshold level, we identified 1197 clouds having 13CO emission and 32 clouds having C18O emission, respectively. We test the stacking bump algorithm in the noise-only datacube, and find that 2 σ thresholds can effectively avoid the possibility of false detection generated by noise. The results proved that the new algorithm has high accuracy and completeness. Statistics of peak intensity, projected angular area, line width, and flux of the clouds show that the power-law indices obtained from different isotopic lines are close to each other.