Cold atomic gas identified by HI self-absorption. Cold atomic clouds toward giant molecular filaments

Abstract

Stars form in the dense interiors of molecular clouds. The dynamics and physical properties of the atomic interstellar medium (ISM) set the conditions under which molecular clouds and eventually stars will form. It is, therefore, critical to investigate the relationship between the atomic and molecular gas phase to understand the global star formation process. Using the high angular resolution data from The HI/OH/Recombination line survey of the Milky Way (THOR), we aim to constrain the kinematic and physical properties of the cold atomic hydrogen gas phase toward the inner Galactic plane. HI self-absorption (HISA) has proven to be a viable method to detect cold atomic hydrogen clouds in the Galactic plane. With the help of a newly developed self-absorption extraction routine (astroSABER), we build upon previous case studies to identify HI self-absorption toward a sample of Giant Molecular Filaments (GMFs). We find the cold atomic gas to be spatially correlated with the molecular gas on a global scale. The column densities of the cold atomic gas traced by HISA are usually of the order of $10^{20}\mathrm{c}{\mathrm{m}}^{-2}$ whereas those of molecular hydrogen traced by ${}^{13}\mathrm{CO}$ are at least an order of magnitude higher. The HISA column densities are attributed to a cold gas component that accounts for a fraction of $\sim$5% of the total atomic gas budget within the clouds. The HISA column density distributions show pronounced log-normal shapes that are broader than those traced by HI emission. The cold atomic gas is found to be moderately supersonic with Mach numbers of a $\sim$few. In contrast, highly supersonic dynamics drive the molecular gas within most filaments.

arXiv comment41 pages, 28 figures, accepted for publication in A&A

References in corpus (70)

• The Neutral Atomic Phases of the ISM in the Galaxy
• The Stellar IMF from Turbulent Fragmentation
• The Interstellar Environment of our Galaxy
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• The Statistics of Supersonic Isothermal Turbulence
• The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
• The Universality of the Stellar IMF
• Large-Scale Structure of the Molecular Gas in Taurus Revealed by High Linear Dynamic Range Spectral Line Mapping
• Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy
• Probing the evolution of molecular cloud structure: From quiescence to birth
• The VLA Galactic Plane Survey
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• Physical properties of molecular clouds for the entire Milky Way disk
• Density probability distribution in one-dimensional polytropic gas dynamics
• A Herschel [CII] Galactic plane survey I: the global distribution of ISM gas components
• One-Point Probability Distribution Functions of Supersonic Turbulent Flows in Self-Gravitating Media
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• Global properties of the HI distribution in the outer Milky Way
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• CO-dark gas and molecular filaments in Milky Way type galaxies
• The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg
• Resolution of the Distance Ambiguity for Galactic HII Regions
• On the evolution of the density pdf in strongly self-gravitating systems
• HI Narrow Line Absorption in Dark Clouds
• Giant Molecular Filaments in the Milky Way
• HI Narrow Self-Absorption in Dark Clouds: Correlations with Molecular Gas and Implications for Cloud Evolution and Star Formation
• Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds
• Three-Dimensional Distribution of the ISM in the Milky Way Galaxy: III. The Total Neutral Gas Disk
• Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure
• ATLASGAL-selected massive clumps in the inner Galaxy: I. CO depletion and isotopic ratios
• Milky Way Kinematics: Measurements at the Subcentral Point of the Fourth Quadrant
• A new density variance - Mach number relation for subsonic and supersonic, isothermal turbulence
• The Physical Properties of Large-Scale Galactic Filaments
• Probing the evolution of molecular cloud structure II: From chaos to confinement
• Autonomous Gaussian Decomposition
• GaussPy+: A fully automated Gaussian decomposition package for emission line spectra
• The Transition from Atomic to Molecular Hydrogen in Interstellar Clouds: 21cm Signature of the Evolution of Cold Atomic Hydrogen in Dense Clouds
• Thermal Phases of the Neutral Atomic Interstellar Medium -- from Solar Metallicity to Primordial Gas
• An application of an optimal statistic for characterising relative orientations
• Understanding star formation in molecular clouds III. Probability distribution functions of molecular lines in Cygnus X
• High CO depletion in southern infrared-dark clouds
• The SEDIGISM survey: Molecular clouds in the inner Galaxy
• THOR - The HI, OH, Recombination Line Survey of the Milky Way - The pilot study: HI observations of the giant molecular cloud W43
• Star-forming content of the giant molecular filaments in the Milky Way
• The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and HI overview
• The HI-to-H2 Transition in a Turbulent Medium
• The Razor's Edge of Collapse: The Transition Point from Lognormal to Powerlaw in Molecular Cloud PDFs
• Histogram of oriented gradients: a technique for the study of molecular cloud formation
• Turbulent Mixing in the Interstellar Medium -- an application for Lagrangian Tracer Particles
• The Lognormal Probability Distribution Function of the Perseus Molecular Cloud: A Comparison of HI and Dust
• Understanding star formation in molecular clouds IV. Column density PDFs from quiescent to massive molecular clouds
• Gaussian decomposition of HI surveys. III. Local HI
• An Improved Technique for Measurement of Cold HI in Molecular Cloud Cores
• The history of dynamics and stellar feedback revealed by the HI filamentary structure in the disk of the Milky Way
• 1420 MHz Continuum Absorption Towards Extragalactic Sources in the Galactic Plane
• The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds
• Exploring the properties of warm and cold atomic hydrogen in the Taurus and Gemini regions
• Cloud formation in the atomic and molecular phase: HI self absorption (HISA) towards a Giant Molecular Filament
• Self-absorption in [CII], ${}^{12}$CO, and HI in RCW120. Building up a geometrical and physical model of the region
• A Neutral Hydrogen Self-Absorption Cloud in the SGPS
• Physical properties of CO-dark molecular gas traced by C${}^{+}$
• Calibrating the HISA temperature: Measuring the temperature of the Riegel-Crutcher cloud
• Autonomous Gaussian decomposition of the Galactic Ring Survey. I. Global statistics and properties of the 13CO emission data
• On the accuracy of HI observations in molecular clouds -- More cold HI than thought?
• The density distribution and physical origins of intermittency in supersonic, highly magnetised turbulence with diverse modes of driving
• Atomic and molecular gas properties during cloud formation
• The Carina Nebula and Gum 31 molecular complex: II. The distribution of the atomic gas revealed in unprecedented detail
• The filamentary structures in the CO emission toward the Milky Way disk

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