The "Maggie" filament: Physical properties of a giant atomic cloud

Abstract

The atomic phase of the interstellar medium plays a key role in the formation process of molecular clouds. Due to the line-of-sight confusion in the Galactic plane that is associated with its ubiquity, atomic hydrogen emission has been challenging to study. Employing the high-angular resolution data from the THOR survey, we identify one of the largest, coherent, mostly atomic HI filaments in the Milky Way at the line-of-sight velocities around -54 km/s. The giant atomic filament "Maggie", with a total length of 1.2 kpc, is not detected in most other tracers, and does not show signs of active star formation. At a kinematic distance of 17 kpc, Maggie is situated below (by 500 pc) but parallel to the Galactic HI disk and is trailing the predicted location of the Outer Arm by 5-10 km/s in longitude-velocity space. The centroid velocity exhibits a smooth gradient of less than $\pm$3 km/s /10 pc and a coherent structure to within $\pm$6 km/s. The line widths of 10 km/s along the spine of the filament are dominated by non-thermal effects. After correcting for optical depth effects, the mass of Maggie's dense spine is estimated to be $7.2\times 10^5{M}_{\odot }$. The mean number density of the filament is 4$\mathrm{c}{\mathrm{m}}^{-3}$, which is best explained by the filament being a mix of cold and warm neutral gas. In contrast to molecular filaments, the turbulent Mach number and velocity structure function suggest that Maggie is driven by transonic to moderately supersonic velocities that are likely associated with the Galactic potential rather than being subject to the effects of self-gravity or stellar feedback. The column density PDF displays a log-normal shape around a mean of $N_{\mathrm{HI}}=4.8\times 10^{20}\mathrm{c}{\mathrm{m}}^{-2}$, thus reflecting the absence of dominating effects of gravitational contraction.

arXiv comment19 pages, 17 figures, accepted for publication in A&A

References in corpus (114)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Theory of Star Formation
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• Planck 2013 results. I. Overview of products and scientific results
• Interstellar Turbulence I: Observations and Processes
• The Neutral Atomic Phases of the ISM in the Galaxy
• The Interstellar Environment of our Galaxy
• Comparing the statistics of interstellar turbulence in simulations and observations: Solenoidal versus compressive turbulence forcing
• Characterizing interstellar filaments with Herschel in IC5146
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• The Relation Between Optical Extinction and Hydrogen Column Density in the Galaxy
• 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
• IRIS: A new generation of IRAS maps
• 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
• 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
• A Parallax-based Distance Estimator for Spiral Arm Sources
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• The Vertical Structure of the Outer Milky Way HI Disk
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• Untangling the Galaxy I: Local Structure and Star Formation History of the Milky Way
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• CO-dark gas and molecular filaments in Milky Way type galaxies
• FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) I: Project Overview and Initial Results
• Lifting the Dusty Veil With Near- and Mid-Infrared Photometry: I. Description and Applications of the Rayleigh-Jeans Color Excess Method
• The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg
• The "Nessie" Nebula: Cluster Formation in a Filamentary Infrared Dark Cloud
• On the nature of star-forming filaments: I. Filament morphologies
• A Galactic-scale gas wave in the Solar Neighborhood
• On the evolution of the density pdf in strongly self-gravitating systems
• HI Narrow Line Absorption in Dark 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
• Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds
• Bending and Breathing Modes of the Galactic Disk
• How long does it take to form a molecular cloud?
• Molecular clouds have power-law probability distribution functions
• The 21-SPONGE HI Absorption Line Survey II: The temperature of Galactic HI
• Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure
• A new density variance - Mach number relation for subsonic and supersonic, isothermal turbulence
• The Cloud Factory I: Generating resolved filamentary molecular clouds from galactic-scale forces
• The Physical Properties of Large-Scale Galactic Filaments
• The Skeleton of the Milky Way
• Probing the evolution of molecular cloud structure II: From chaos to confinement
• New Temperatures of Diffuse Interstellar Gas: Thermally Unstable Gas
• The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results
• Fitting Together the HI Absorption and Emission in the SGPS
• A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey
• The Outer Disk of the Milky Way Seen in 21-cm Absorption
• 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
• Galactocentric variation of the gas-to-dust ratio and its relation with metallicity
• The structure of the thermally bistable and turbulent atomic gas in the local interstellar medium
• Cold Milky Way Hi gas in filaments
• Analytic HI-to-H2 Photodissociation Transition Profiles
• Thermal Phases of the Neutral Atomic Interstellar Medium -- from Solar Metallicity to Primordial Gas
• A Census of Large-Scale ($\ge$ 10 pc), Velocity-Coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree
• Understanding star formation in molecular clouds III. Probability distribution functions of molecular lines in Cygnus X
• Two chemically similar stellar overdensities on opposite sides of the plane of the Galaxy
• What can simulated molecular clouds tell us about real molecular clouds?
• The CARMA-NRO Orion Survey: The filamentary structure as seen in C${}^{18}$O emission
• Ubiquitous velocity fluctuations throughout the molecular interstellar medium
• Giant molecular filaments in the Milky Way II: The fourth Galactic quadrant
• ROHSA: Regularized Optimization for Hyper-Spectral Analysis - Application to phase separation of 21 cm data
• THOR - The HI, OH, Recombination Line Survey of the Milky Way - The pilot study: HI observations of the giant molecular cloud W43
• 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
• The Lognormal Probability Distribution Function of the Perseus Molecular Cloud: A Comparison of HI and Dust
• Turbulent Mixing in the Interstellar Medium -- an application for Lagrangian Tracer Particles
• The Interstellar Medium and star formation on kpc size scales
• The temperature of the diffuse HI in the Milky Way I: High resolution HI 21 cm absorption studies
• The temperature of the diffuse HI in the Milky Way II: Gaussian decomposition of the HI 21 cm absorption spectra
• Forced turbulence in thermally bistable gas: A parameter study
• The evolution of Giant Molecular Filaments
• 3D chemical structure of diffuse turbulent ISM. I. Statistics of the HI-to-H${}_2$ transition
• On the shape and completeness of the column density probability distribution function of molecular clouds
• The reliability of observational measurements of column density probability distribution functions
• Radio continuum emission in the northern Galactic plane: Sources and spectral indices from the THOR survey
• The history of dynamics and stellar feedback revealed by the HI filamentary structure in the disk of the Milky Way
• Spontaneous generation of bending waves in isolated Milky Way-like discs
• 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
• HI-to-H2 Transition Layers in the Star-Forming Region W43
• OB Stars in the Solar Neighborhood I: Analysis of their Spatial Distribution
• Excitation temperature of the warm neutral medium as a new probe of the Lyman-α radiation field
• 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
• Thermal and turbulent properties of the Warm Neutral Medium in the solar neighborhood
• Physical properties of CO-dark molecular gas traced by C${}^{+}$
• OH absorption in the first quadrant of the Milky Way as seen by THOR
• Dense Gas in a Giant Molecular Filament
• How do velocity structure functions trace gas dynamics in simulated molecular clouds?
• 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
• OH Survey along Sightlines of Galactic Observations of Terahertz C+
• The Cloud Factory II: Gravoturbulent Kinematics of Resolved Molecular Clouds in a Galactic Potential
• Estimating kinetic temperature from H I 21 cm absorption studies: correction for the turbulence broadening
• Turbulent power spectrum in warm and cold neutral medium using the Galactic HI 21 cm emission
• FOREST unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope (FUGIN). VII. molecular fraction of HI clouds

Cited by in corpus (3)

• PHANGS-JWST First Results: Tracing the Diffuse ISM with JWST Imaging of Polycyclic Aromatic Hydrocarbon Emission in Nearby Galaxies
• The Galactic dynamics revealed by the filamentary structure in atomic hydrogen emission
• PHANGS-JWST First Results: The Dust Filament Network of NGC 628 and its Relation to Star Formation Activity