The Carina Nebula and Gum 31 molecular complex: II. The distribution of the atomic gas revealed in unprecedented detail

Abstract

We report high spatial resolution observations of the HI 21cm line in the Carina Nebula and the Gum 31 region obtained with the Australia Telescope Compact Array. The observations covered $\sim$ 12 deg${}^2$ centred on $l=287.5°,b=-1°$, achieving an angular resolution of $\sim$ 35 arcseconds. The HI map revealed complex filamentary structures across a wide range of velocities. Several "bubbles" are clearly identified in the Carina Nebula Complex, produced by the impact of the massive star clusters located in this region. An HI absorption profile obtained towards the strong extragalactic radio source PMN J1032--5917 showed the distribution of the cold component of the atomic gas along the Galactic disk, with the Sagittarius-Carina and Perseus spiral arms clearly distinguishable. Preliminary calculations of the optical depth and spin temperatures of the cold atomic gas show that the HI line is opaque ($\tau \gtrsim$ 2) at several velocities in the Sagittarius-Carina spiral arm. The spin temperature is $\sim 100$ K in the regions with the highest optical depth, although this value might be lower for the saturated components. The atomic mass budget of Gum 31 is $\sim 35\%$ of the total gas mass. HI self absorption features have molecular counterparts and good spatial correlation with the regions of cold dust as traced by the infrared maps. We suggest that in Gum 31 regions of cold temperature and high density are where the atomic to molecular gas phase transition is likely to be occurring.

20 pages, 1 table, 16 Figures, Accepted for Publication in the Monthly Notices of the Royal Astronomical Society Journal

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• The Molonglo Galactic Plane Survey (MGPS-2): Compact Source Catalogue
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• Milky Way Kinematics: Measurements at the Subcentral Point of the Fourth Quadrant
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Cited by in corpus (12)

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• Effect of feedback of massive stars in the fragmentation, distribution, and kinematics of the gas in two star forming regions in the Carina Nebula
• Probing ISM Structure in Trumpler 14 & Carina I Using The Stratospheric Terahertz Observatory 2
• Massive star formation in the Carina nebula complex and Gum 31 -- I. The Carina nebula complex
• Atomic and molecular gas properties during cloud formation
• The "Maggie" filament: Physical properties of a giant atomic cloud
• The Carina Nebula and Gum 31 molecular complex III: The distribution of the 1-3 GHz radio continuum across the whole nebula
• Cold atomic gas identified by HI self-absorption. Cold atomic clouds toward giant molecular filaments
• Massive star formation in the Carina nebula complex and Gum 31 -- II. a cloud-cloud collision in Gum 31
• Probing Polarization and the Role of Magnetic Fields in Cloud Destruction in the Keyhole Nebula