The G332 Molecular Cloud

• Main Author: Romano, Domenico
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UNSW, Sydney 2020
• Subjects: Interstellar Medium; Astrophysics; Molecular cloud; 12CO; Interstellar molecules; Intestellar cloud; mm astronomy; anzsrc-for: 510104 Galactic astronomy; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/1959.4/100692; https://unsworks.unsw.edu.au/bitstreams/6fda1035-8e8c-4415-8915-70b5c3e3bfb2/download; https://doi.org/10.26190/unsworks/24399

This thesis presents a morphological study and physical analysis of a new Giant Molecular Cloud (GMC) discovered using a survey of the Galactic Plane in the lines of the carbon monoxide isotopologues (12CO, 13CO, C18O J = 1 → 0) undertaken with the 22m Mopra radio telescope (Mopra CO Southern Galactic Plane Survey, Mopra CO SGPS). The Mopra survey was supplemented with neutral carbon maps from the HEAT telescope in Antarctica. The new GMC (hereinafter the G332 ring) covers the sky region 332◦ < ℓ < 333◦ and b = ±0.5◦ (hereinafter the G332 region). The mass of the ring is determined to be ∼ 2 × 105M⊙, and its distance is estimated to be ∼ 3.7 kpc from the Sun. The ring exhibits emission with broadly similar morphology in the emission lines of CO and the [CI] 3P2 →3 P1 line transition at 809.342 GHz, as well as in far-IR dust emission. The dark molecular gas fraction — estimated from the 13CO and [CI] line emission — is ∼ 16% assuming a Tex of 20K. Comparing the [CI] integrated intensity and N(H2) traced by 13CO and 12CO, we define an X809 CI factor, analogous to the usual Xco. X809 CI ranges between (1.8–2.0)×1021cm−2K−1km−1s. Local variations in Xco and Tex were examined across the cloud. In regions where the star formation activity is not in an advanced state, an increase is found in the mean value and dispersion of the Xco factor as the excitation temperature decreases. A strong spatial correspondence was found between the molecular structure and the number of infrared dark clouds (IRDCs), the angular positions of which follow the C18O emission. A catalogue of C18O clumps within the cloud, and their physical characteristics, was created. The star formation (SF) activity ongoing in the cloud shows a correlation with Tex, [CI] and CO emissions, and an anti-correlation with Xco, and suggests a North-South spatial gradient in the SF activity. Regarding dust emission, we present a new approach to disentangling dust emission across the Galaxy, using the velocity information from [HI] and 13CO data. The ...