GASKAP Pilot Survey Science II: ASKAP Zoom Observations of Galactic 21-cm Absorption

Abstract

Using the Australian Square Kilometre Array Pathfinder to measure 21-cm absorption spectra toward continuum background sources, we study the cool phase of the neutral atomic gas in the far outer disk, and in the inner Galaxy near the end of the Galactic bar at longitude 340 degrees. In the inner Galaxy the cool atomic gas has a smaller scale height than in the solar neighborhood, similar to the molecular gas and the superthin stellar population in the bar. In the outer Galaxy the cool atomic gas is mixed with the warm, neutral medium, with the cool fraction staying roughly constant with Galactic radius. The mean spin temperature, i.e. the ratio of the emission brightness temperature to the absorption, is roughly constant for velocities corresponding to Galactic radius greater than about twice the solar circle radius. The ratio has a value of about 300 K, but this does not correspond to a physical temperature in the gas. If the gas causing the absorption has kinetic temperature of about 100 K, as in the solar neighborhood, then the value 300 K indicates that the fraction of the gas mass in this phase is one-third of the total HI mass.

arXiv comment29 pages, 12 figures, submitted to Astrophysical Journal

References in corpus (66)

• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• The ATNF Pulsar Catalogue
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• The Neutral Atomic Phases of the ISM in the Galaxy
• The Circumgalactic Medium
• The Interstellar Environment of our Galaxy
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
• Gaseous Galaxy Halos
• Physical properties of molecular clouds for the entire Milky Way disk
• The Structure of the Milky Way's Bar Outside the Bulge
• GASS: The Parkes Galactic All-Sky Survey. I. Survey Description, Goals, and Initial Data Release
• The Southern Galactic Plane Survey: HI Observations and Analysis
• Australian Square Kilometre Array Pathfinder: I. System Description
• A revised catalogue of 294 Galactic supernova remnants
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• Molecular cloud evolution. I. Molecular cloud and thin CNM sheet formation
• Global properties of the HI distribution in the outer Milky Way
• GASS: The Parkes Galactic All-Sky Survey. II. Stray-Radiation Correction and Second Data Release
• Resolving small-scale cold circumgalactic gas in TNG50
• Orbiting Circum-galactic Gas as a Signature of Cosmological Accretion
• The COS/UVES Absorption Survey of the Magellanic Stream. III: Ionization, Total Mass, and Inflow Rate onto the Milky Way
• The Spin Temperature of Warm Interstellar H I
• The Southern Galactic Plane Survey: Polarized Radio Continuum Observations and Analysis
• The Vertical Distribution and Kinematics of HI and Mass Models of the Galactic Disk
• The 21-SPONGE HI Absorption Line Survey II: The temperature of Galactic HI
• Kinematic Distances: A Monte Carlo Method
• ATLASGAL --- Complete compact source catalogue: 280\degr\ $<\ell <$ 60\degr
• The spin temperature of high-redshift damped Lyman-$\alpha$ systems
• The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results
• GASKAP -- The Galactic ASKAP Survey
• Fitting Together the HI Absorption and Emission in the SGPS
• Finding Distant Galactic HII Regions
• Kinematics of Circumgalactic Gas: Feeding Galaxies and Feedback
• The Outer Disk of the Milky Way Seen in 21-cm Absorption
• Source-finding for the Australian Square Kilometre Array Pathfinder
• Metallicity Structure in the Milky Way Disk Revealed by Galactic HII Regions
• Cold and warm atomic gas around the Perseus molecular cloud I: Basic Properties
• Gas infall and radial transport in cosmological simulations of Milky Way-mass disks
• Tracing the Spiral Structure of the Outer Milky Way with Dense Atomic Hydrogen Gas
• GASKAP-HI Pilot Survey Science I: ASKAP Zoom Observations of HI Emission in the Small Magellanic Cloud
• Two-phase equilibrium and molecular hydrogen formation in damped Lyman-alpha systems
• Exploring the properties of warm and cold atomic hydrogen in the Taurus and Gemini regions
• Extracting the cold neutral medium from HI emission with deep learning: Implications for Galactic foregrounds at high latitude
• Ly-alpha Radiative Transfer: Monte-Carlo Simulation of the Wouthuysen-Field Effect
• In search of cool flow accretion onto galaxies $-$ where does the disk gas end?
• Chemical Abundances in a Turbulent Medium -- H${}_2$, OH${}^{+}$, H${}_2$O${}^{+}$, ArH${}^{+}$
• Shock-multicloud interactions in galactic outflows -- I. Cloud layers with log-normal density distributions
• Green Bank Telescope observations of low column density HI around NGC 2997 and NGC 6946
• A GBT Survey of the HALOGAS Galaxies and Their Environments I: Revealing the full extent of HI around NGC891, NGC925, NGC4414 & NGC4565
• Molecular gas distribution perpendicular to the Galactic plane
• Structure of the outer Galactic disc with Gaia-DR2
• Detection of the diffuse HI emission in the Circumgalactic Medium of NGC 891 and NGC 4565
• An ATCA Survey of HI Absorption in the Magellanic Clouds I: HI Gas Temperature Measurements in the Small Magellanic Cloud
• Cooling flows around cold clouds in the circumgalactic medium: steady-state models & comparison with TNG50
• Milky Way Kinematics. II. A uniform inner Galaxy HI terminal velocity curve
• A Census of the Extended Neutral Hydrogen Around 18 MHONGOOSE Galaxies
• Giant Metrewave Radio Telescope detection of two new HI 21cm absorbers at $z\approx 2$
• A statistical measurement of the HI spin temperature in DLAs at cosmological distances
• Evolutionary Map of the Universe (EMU):Compact radio sources in the SCORPIO field towards the Galactic plane
• Gas accretion in Milky Way-like galaxies: temporal and radial dependencies
• A New Multi-Tracer Approach to Defining the Spiral arm width in the Milky Way
• Cold HI ejected into the Magellanic Stream
• The MACH HI absorption survey I: Physical conditions of cold atomic gas outside of the Galactic plane

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• The Galactic dynamics revealed by the filamentary structure in atomic hydrogen emission
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• The FAST HI 21-cm absorption blind survey. II. -- Statistic Exploration for Associated and Intervening systems
• The MeerKAT Absorption Line Survey (MALS) data release 3: Cold atomic gas associated with the Milky Way
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