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

Abstract

We present results of cloud catalogs of 12CO, 13CO, and C18O (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 12CO, 13CO, and C18O from the position–position–velocity (PPV) data cubes. 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. Above the 2σ threshold level, we identified 1197 clouds having 13CO emission and 32 clouds having C18O emission. We test the stacking bump algorithm in the noise-only datacube and find that the 2σ 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.

The Molecular Clouds in a Section of the Third Galactic Quadrant: Observational Properties and Chemical Abundance Ratio between CO and its Isotopologues

“…The data cover a section in the third Galactic quadrant (195°< l < 220°, |b| < 5°) and are part of the Milky Way Imaging Scroll Painting (MWISP) project, which is a multiline Galactic plane survey in CO and its isotopic transitions. The mean noise σ is ∼0.45 K for 12 CO with 0.16 km s −1 velocity resolution and ∼0.25 K for 13 CO and C 18 O with 0.17 km s −1 velocity resolution (Wang et al 2023).…”

“…This paper is the third in a series of studies on large samples of MCs in this region. In Paper I (Wang et al 2023), the data were described in detail, and 7069 clouds were identified based on the DBSCAN algorithm in the 12 CO data. Additionally, we identified 1197 clouds with 13 CO emission and 32 clouds with C 18 O emission based on the stacking bump algorithm in the catalog of 7069 clouds.…”

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

“…Oliver et al (1996) performed a detailed CO study toward the Mon OB1 region based on the CfA 1.2 m telescope. The distribution of column density and the abundance ratio of molecular gas (C 18 O/ 13 CO) in the region were also investigated recently (Ma et al 2022;Wang et al 2023a).…”

“…We also try to estimate the mass of dense gas traced by C 18 O. Here we use the stacking bump algorithm (Wang et al 2023a) to search for the C 18 O signal within the 13 CO boundary. Briefly, the identified C 18 O signal satisfies the following conditions: (1) For each identified pixel, at least three continuous channels of the spectrum are larger than two times the rms noise (∼0.5 K).…”

“…(3) The average spectrum of identified C 18 O structures has three continuous channels above three times the noise of the average spectrum. According to Wang et al (2023a), the stacking bump algorithm can effectively avoid false detections generated by noise and can find weak but reliable C 18 O signal. In total, the C 18 O emission area makes up 3.2% of the 12 CO emission area.…”