The Molecular Clouds in a Section of the Third Galactic Quadrant: Cloud Catalog

Abstract

We present results of cloud catalogs of ^12 CO, ^13 CO, and C ^18 O ( J = 1–0) in a section of the third Galactic quadrant over (195° < l < 220°, ∣ b ∣ < 5°) from the Milky Way Imaging Scroll Painting project. The data were acquired with the PMO 13.7 m millimeter telescope with ∼50″angular resolution. We construct three molecular cloud catalogs containing information of ^12 CO, ^13 CO, and C ^18 O from the position–position–velocity (PPV) data cubes. The ^12 CO cloud catalog contains 7069 samples identified based on the DBSCAN algorithm. We develop a new algorithm, the stacking bump algorithm, for identifying ^13 CO and C ^18 O emission by searching for weak signals in the original spectra of ^13 CO and C ^18 O within the boundary in PPV space defined by the ^12 CO cloud. Above the 2 σ threshold level, we identified 1197 clouds having ^13 CO emission and 32 clouds having C ^18 O emission. We test the stacking bump algorithm in the noise-only datacube and find that the 2 σ threshold 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.

Keywords

• Molecular gas
• Molecular clouds