Compressed magnetized shells of atomic gas and the formation of the Corona Australis molecular cloud

Abstract

We present the identification of the previously unnoticed physical association between the Corona Australis molecular cloud (CrA), traced by interstellar dust emission, and two shell-like structures observed with line emission of atomic hydrogen (HI) at 21 cm. Although the existence of the two shells had already been reported in the literature, the physical link between the HI emission and CrA was never highlighted before. We use both Planck and Herschel data to trace dust emission and the Galactic All Sky HI Survey (GASS) to trace HI. The physical association between CrA and the shells is assessed based both on spectroscopic observations of molecular and atomic gas and on dust extinction data with Gaia. The shells are located at a distance between 140 and 190 pc, comparable to the distance of CrA, which we derive as 150.5 +- 6.3 pc. We also employ dust polarization observations from Planck to trace the magnetic-field structure of the shells. Both of them show patterns of magnetic-field lines following the edge of the shells consistently with the magnetic-field morphology of CrA. We estimate the magnetic-field strength at the intersection of the two shells via the Davis-Chandrasekhar-Fermi (DCF) method. Albeit the many caveats that are behind the DCF method, we find a magnetic-field strength of 27 +- 8 $\mu$G, at least a factor of two larger than the magnetic-field strength computed off of the HI shells. This value is also significantly larger compared to the typical values of a few $\mu$G found in the diffuse HI gas from Zeeman splitting. We interpret this as the result of magnetic-field compression caused by the shell expansion. This study supports a scenario of molecular-cloud formation triggered by supersonic compression of cold magnetized HI gas from expanding interstellar bubbles.

arXiv comment11 pages, 10 figures, Accepted for publication by A&A on October 20, 2020

References in corpus (57)

• The Milky Way in Molecular Clouds: A New Complete CO Survey
• From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey
• The Neutral Atomic Phases of the ISM in the Galaxy
• Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models
• Planck 2013 results. XI. All-sky model of thermal dust emission
• Gaia Data Release 2: using Gaia parallaxes
• Herschel view of the Taurus B211/3 filament and striations: Evidence of filamentary growth?
• The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
• Gaia Data Release 2: first stellar parameters from Apsis
• Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds
• Physical properties of molecular clouds for the entire Milky Way disk
• GASS: The Parkes Galactic All-Sky Survey. I. Survey Description, Goals, and Initial Data Release
• Turbulent molecular clouds
• The Millennium Arecibo 21-cm Absorption Line Survey. IV. Statistics of Magnetic Field, Column Density, and Turbulence
• The Origin of the Magellanic Stream and Its Leading Arm
• The Formation and Destruction of Molecular Clouds and Galactic Star Formation
• Planck Early Results: Thermal dust in Nearby Molecular Clouds
• A Compendium of Distances to Molecular Clouds in the Star Formation Handbook
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• Characterizing the properties of nearby molecular filaments observed with Herschel
• GASS: The Parkes Galactic All-Sky Survey. II. Stray-Radiation Correction and Second Data Release
• Reconstructing the density and temperature structure of prestellar cores from $Herschel$ data: A case study for B68 and L1689B
• GASS: The Parkes Galactic All-Sky Survey. Update: improved correction for instrumental effects and new data release
• A new, large-scale map of interstellar reddening derived from HI emission
• The Fate of High-Velocity Clouds: Warm or Cold Cosmic Rain?
• Magnetohydronamic Evolution of HII Regions in Molecular Clouds: Simulation Methodology, Tests, and Uniform Media
• The molecular cloud lifecycle
• Neutral hydrogen structures trace dust polarization angle: Implications for cosmic microwave background foregrounds
• Properties of the dense core population in Orion B as seen by the Herschel Gould Belt survey
• Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
• The Galactic Distribution of Large HI Shells
• The Herschel view of the dense core population in the Ophiuchus molecular cloud
• Distances and Kinematics of Gould Belt Star-Forming Regions with Gaia DR2 results
• Using Herschel and Planck observations to delineate the role of magnetic fields in molecular cloud structure
• The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results
• GHIGLS: HI mapping at intermediate Galactic latitude using the Green Bank Telescope
• Alignment of Irregular Grains by Mechanical Torques
• GaussPy+: A fully automated Gaussian decomposition package for emission line spectra
• Supergiant Shells and Molecular Cloud Formation in the LMC
• Probing accretion of ambient cloud material into the Taurus B211/B213 filament
• From diffuse gas to dense molecular cloud cores
• The Physical Nature of Neutral Hydrogen Intensity Structure
• ROHSA: Regularized Optimization for Hyper-Spectral Analysis - Application to phase separation of 21 cm data
• Corona-Australis DANCe. I. Revisiting the census of stars with Gaia-DR2 data
• Probing changes of dust properties along a chain of solar-type prestellar and protostellar cores in Taurus with NIKA
• The Distances to Molecular Clouds at High Galactic Latitudes based on GAIA DR2
• The dense cores and filamentary structure of the molecular cloud in Corona Australis. Herschel SPIRE and PACS observations from the Herschel Gould Belt Survey
• The role of magnetic fields in the structure and interaction of supershells
• The magnetic environment of the Orion-Eridanus superbubble as revealed by Planck
• Modelling and simulation of large-scale polarized dust emission over the southern Galactic cap using the GASS HI data
• Planck intermediate results. XXXIV. The magnetic field structure in the Rosette Nebula
• Gas shells and magnetic fields in the Orion-Eridanus superbubble
• A Young GMC Formed at the Interface of Two Colliding Supershells: Observations Meet Simulations
• Is there a left-handed magnetic field in the solar neighborhood? Exploring helical magnetic fields in the interstellar medium through dust polarization power spectra
• Dust polarization modeling at large-scale over the Northern Galactic cap using EBHIS and Planck data
• Fourier-space combination of Planck and Herschel images
• GSH 006-15+7: A local Galactic supershell featuring transition from HI emission to absorption

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