Cloud formation in the atomic and molecular phase: HI self absorption (HISA) towards a Giant Molecular Filament

Abstract

Molecular clouds form from the atomic phase of the interstellar medium. However, characterizing the transition between the atomic and the molecular interstellar medium (ISM) is a difficult observational task. Here we address cloud formation processes by combining HSIA with molecular line data. One scenario proposed by numerical simulations is that the column density probability density functions (N-PDF) evolves from a log-normal shape at early times to a power-law-like shape at later times. In this paper, we study the cold atomic component of the giant molecular filament GMF38a (d=3.4 kpc, length$\sim 230$ pc). We identify an extended HISA feature, which is partly correlated with the 13CO emission. The peak velocities of the HISA and 13CO observations agree well on the eastern side of the filament, whereas a velocity offset of approximately 4 km s${}^{-1}$ is found on the western side. The sonic Mach number we derive from the linewidth measurements shows that a large fraction of the HISA, which is ascribed to the cold neutral medium (CNM), is at subsonic and transonic velocities. The column density of the CNM is on the order of 10${}^{20}$ to 10${}^{21}$ cm${}^{-2}$. The column density of molecular hydrogen is an order of magnitude higher. The N-PDFs from HISA (CNM), HI emission (WNM+CNM), and 13CO (molecular component) are well described by log-normal functions, which is in agreement with turbulent motions being the main driver of cloud dynamics. The N-PDF of the molecular component also shows a power law in the high column-density region, indicating self-gravity. We suggest that we are witnessing two different evolutionary stages within the filament. The eastern subregion seems to be forming a molecular cloud out of the atomic gas, whereas the western subregion already shows high column density peaks, active star formation and evidence of related feedback processes.

arXiv comment22 pages, 25 figures, accepted for publication by A&A

References in corpus (93)

• Planck 2015 results. XIII. Cosmological parameters
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Theory of Star Formation
• The Cosmic Microwave Background Spectrum from the Full COBE/FIRAS Data Set
• The Temperature of the Cosmic Microwave Background
• The Neutral Atomic Phases of the ISM in the Galaxy
• Powerlaw: a Python package for analysis of heavy-tailed distributions
• Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models
• Comparing the statistics of interstellar turbulence in simulations and observations: Solenoidal versus compressive turbulence forcing
• The Star Formation Rate of Turbulent Magnetized Clouds: Comparing Theory, Simulations, and Observations
• ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns
• The Relation Between Optical Extinction and Hydrogen Column Density in the Galaxy
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• The Atomic to Molecular Transition in Galaxies. II: HI and H_2 Column Densities
• Probing the evolution of molecular cloud structure: From quiescence to birth
• The VLA Galactic Plane Survey
• The WISE Catalog of Galactic HII Regions
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• The Physics of Star Formation
• ATLASGAL --- properties of a complete sample of Galactic clumps
• Physical Properties and Galactic Distribution of Molecular Clouds identified in the Galactic Ring Survey
• Turbulent molecular clouds
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• A Parallax-based Distance Estimator for Spiral Arm Sources
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• On the Density Distribution in Star-forming Interstellar Clouds
• Global properties of the HI distribution in the outer Milky Way
• The Atomic to Molecular Transition in Galaxies. I: An Analytic Approximation for Photodissociation Fronts in Finite Clouds
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) I: Project Overview and Initial Results
• The "Nessie" Nebula: Cluster Formation in a Filamentary Infrared Dark Cloud
• Gravity or turbulence? II. Evolving column density PDFs in molecular clouds
• HI Narrow Line Absorption in Dark Clouds
• High-dynamic-range extinction mapping of infrared dark clouds: Dependence of density variance with sonic Mach number in molecular clouds
• Large-scale filaments associated with Milky Way spiral arms
• Multi-temperature mapping of dust structures throughout the Galactic Plane using the PPMAP tool with Herschel Hi-GAL data
• Giant Molecular Filaments in the Milky Way
• The Bones of the Milky Way
• HI Narrow Self-Absorption in Dark Clouds: Correlations with Molecular Gas and Implications for Cloud Evolution and Star Formation
• How long does it take to form a molecular cloud?
• Evolution of column density distributions within Orion~A
• Molecular clouds have power-law probability distribution functions
• ATLASGAL-selected massive clumps in the inner Galaxy: I. CO depletion and isotopic ratios
• Class 0 Protostars in the Perseus Molecular Cloud: A Correlation Between the Youngest Protostars and the Dense Gas Distribution
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• A high-dispersion molecular gas component in nearby galaxies
• ATLASGAL -- A Galaxy-wide sample of dense filamentary structures
• Galactic Supernova Remnant Candidates Discovered by THOR
• Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
• The Physical Properties of Large-Scale Galactic Filaments
• The Skeleton of the Milky Way
• Detection of two power-law tails in the probability distribution functions of massive GMCs
• HI and CO Velocity Dispersions in Nearby Galaxies
• A Self-Absorption Census of Cold HI Clouds in the Canadian Galactic Plane Survey
• Autonomous Gaussian Decomposition
• The Transition from Atomic to Molecular Hydrogen in Interstellar Clouds: 21cm Signature of the Evolution of Cold Atomic Hydrogen in Dense Clouds
• Cold and Warm Atomic Gas around the Perseus Molecular Cloud. II. The Impact of High Optical Depth on the HI Column Density Distribution and Its Implication for the HI-to-H2 Transition
• A Census of Large-Scale ($\ge$ 10 pc), Velocity-Coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree
• Herschel's view of the large-scale structure in the Chamaeleon dark clouds
• Understanding star formation in molecular clouds III. Probability distribution functions of molecular lines in Cygnus X
• The shapes of column density PDFs - The importance of the last closed contour
• Observational Diagnostics of Self-Gravitating MHD Turbulence in Giant Molecular Clouds
• The ${}^{12}$CO/${}^{13}$CO ratio in turbulent molecular clouds
• The X_CO conversion factor from galactic multiphase ISM simulations
• Giant molecular filaments in the Milky Way II: The fourth Galactic quadrant
• 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
• Histogram of oriented gradients: a technique for the study of molecular cloud formation
• The Lognormal Probability Distribution Function of the Perseus Molecular Cloud: A Comparison of HI and Dust
• The Anatomy of the Column Density Probability Distribution Function (N-PDF)
• CO line ratios in molecular clouds: the impact of environment
• CO-dark gas and molecular filaments in Milky Way-type galaxies - II: The temperature distribution of the gas
• Diffuse Molecular Cloud Densities from UV Measurements of CO Absorption
• Cloud structure of three Galactic infrared dark star-forming regions from combining ground and space based bolometric observations
• How well does CO emission measure the H${}_2$ mass of MCs?
• Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function
• The reliability of observational measurements of column density probability distribution functions
• "Missing Link" Clouds in the Southern Galactic Plane Survey
• On the shape and completeness of the column density probability distribution function of molecular clouds
• An Improved Technique for Measurement of Cold HI in Molecular Cloud Cores
• Radio continuum emission in the northern Galactic plane: Sources and spectral indices from the THOR survey
• The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds
• HI-to-H2 Transition Layers in the Star-Forming Region W43
• A Neutral Hydrogen Self-Absorption Cloud in the SGPS
• An Automated Method for the Detection and Extraction of HI Self-Absorption in High-Resolution 21cm Line Surveys
• Power-law tails in probability density functions of molecular cloud column density
• Calibrating the HISA temperature: Measuring the temperature of the Riegel-Crutcher cloud
• Relationship between the column density distribution and evolutionary class of molecular clouds as viewed by ATLASGAL
• The Carina Nebula and Gum 31 molecular complex: II. The distribution of the atomic gas revealed in unprecedented detail
• Catching the Birth of a Dark Molecular Cloud for the First Time

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