The discovery of the largest gas filament in our Galaxy, or a new spiral arm?

Abstract

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we detect a giant HI filamentary structure in the sky region of 307$.{}^{\circ }$7 $<$ $\alpha$ $<$ 311$.{}^{\circ }$0 and 40$.{}^{\circ }$9 $<$ $\delta$ $<$ 43$.{}^{\circ }$4. The structure has a velocity range of $-$170 km s${}^{-1}$ to $-$130 km s${}^{-1}$, and a mean velocity of $-$150 km s${}^{-1}$, putting it to a Galactocentric distance of 22 kpc. The HI structure has a length of 1.1 kpc, which appears to be so far the furthest and largest giant filament in the Galaxy and we name it Cattail. Its mass is calculated to be 6.5 $\times$ 10${}^4$ M${}_{\odot }$ and the linear mass density is 60 M${}_{\odot }$ pc${}^{-1}$. Its width is 207 pc, corresponding to an aspect ratio of 5:1. Cattail possesses a small velocity gradient (0.02 km s${}^{-1}$ pc${}^{-1}$) along its major axis. Together with the HI4PI data, we find that Cattail could have an even larger length, up to 5 kpc. We also identify another new elongated structure to be the extension into the Galactic first quadrant of the Outer Scutum-Centaurus (OSC) arm, and Cattail appears to be located far behind the OSC. The question about how such a huge filament is produced at the extreme Galactic location remains open. Alternatively, Cattail might be part of a new arm beyond the OSC, though it is puzzling that the structure does not fully follow the warp of the Galactic disk.

arXiv comment10 pages, 7 figures, Accepted for publication in ApJL

References in corpus (59)

• The observed properties of dwarf galaxies in and around the Local Group
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• The Circumgalactic Medium
• Filamentary structure of star-forming complexes
• Gaseous Galaxy Halos
• The WISE Catalog of Galactic HII Regions
• GASS: The Parkes Galactic All-Sky Survey. I. Survey Description, Goals, and Initial Data Release
• Dynamic star formation in the massive DR21 filament
• Cluster-formation in the Rosette molecular cloud at the junctions of filaments
• The Fundamental Performance of FAST with 19-beam Receiver at L Band
• Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region
• Helical Fields and Filamentary Molecular Clouds
• Considerations for a Multi-beam Multi-purpose Survey with FAST
• A Parallax-based Distance Estimator for Spiral Arm Sources
• Filamentary structures and compact objects in the Aquila and Polaris clouds observed by Herschel
• The Vertical Structure of the Outer Milky Way HI Disk
• CO-dark gas and molecular filaments in Milky Way type galaxies
• GASS: The Parkes Galactic All-Sky Survey. II. Stray-Radiation Correction and Second Data Release
• The "Nessie" Nebula: Cluster Formation in a Filamentary Infrared Dark Cloud
• The Effelsberg-Bonn HI Survey: Milky Way gas. First data release
• ON the Nature of the Local Spiral Arm of the Milky Way
• On the nature of star-forming filaments: I. Filament morphologies
• Dark matter in the Milky Way, II. the HI gas distribution as a tracer of the gravitational potential
• Physical properties of interstellar filaments
• GASS: The Parkes Galactic All-Sky Survey. Update: improved correction for instrumental effects and new data release
• Large-scale filaments associated with Milky Way spiral arms
• Giant Molecular Filaments in the Milky Way
• The Bones of the Milky Way
• The Fate of High-Velocity Clouds: Warm or Cold Cosmic Rain?
• The Source of Ionization along the Magellanic Stream
• Spurs and feathering in spiral galaxies
• The Effelsberg-Bonn HI Survey (EBHIS)
• A Molecular Spiral Arm in the Far Outer Galaxy
• The Physical Properties of Large-Scale Galactic Filaments
• The Skeleton of the Milky Way
• A closer look at the "characteristic" width of molecular cloud filaments
• A Possible Extension of the Scutum-Centaurus Arm into the Outer Second Quadrant
• Cold Milky Way Hi gas in filaments
• A Census of Large-Scale ($\ge$ 10 pc), Velocity-Coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree
• 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
• Giant molecular filaments in the Milky Way II: The fourth Galactic quadrant
• Simulations of High-Velocity Clouds. I. Hydrodynamics and High-Velocity High Ions
• 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/OH/Recombination line survey of the inner Milky Way (THOR)
• Head-Tail Clouds: Drops to Probe the Diffuse Galactic Halo
• High Velocity Cloud Complex H: A Satellite of the Milky Way in a Retrograde Orbit?
• The history of dynamics and stellar feedback revealed by the HI filamentary structure in the disk of the Milky Way
• HI filaments are cold and associated with dark molecular gas. HI4PI based estimates of the local diffuse CO-dark H2 distribution
• A large-scale survey of CO and its isotopologues toward the Rosette molecular cloud
• The Dense Filamentary Giant Molecular Cloud G23.0-0.4: Birthplace of Ongoing Massive Star Formation
• The Serpens filament: at the onset of slightly supercritical collapse
• CO~($J=1-0$) Observations of a Filamentary Molecular Cloud in the Galactic Region Centered at $l = 150\arcdeg, b = 3.5\arcdeg$
• Exploring Hydrodynamic Instabilities along the Infalling High-Velocity Cloud Complex A
• Discovery of a distant molecular cloud in the extreme outer Galaxy with the Nobeyama 45-m telescope
• The Molecular Clouds associated with the H II Regions/Candidates between $l=207.7^{\circ }$ and $l=211.7^{\circ }$

Cited by in corpus (6)

• 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
• A global view on star formation: The GLOSTAR Galactic plane survey VIII. Formaldehyde absorption in Cygnus~X
• Peering into the Milky Way by FAST: I. Exquisite HI structures in the inner Galactic disk from the piggyback line observations of the FAST GPPS survey
• Neutral hydrogen filaments in interstellar media: Are they physical?
• Molecular Clouds in the Galactic Plane from $l$ = [59.75${}^{\circ }$, 74.75${}^{\circ }$] and $b$ = [$-$5.25${}^{\circ }$, +5.25${}^{\circ }$]