Dickey, JM, Dempsey, JM, Pingel, NM, McClure-Griffiths, NM, Jameson, K, Dawson, JR, Denes, H, Clark, SE, Joncas, G, Leahy, D, Lee, M-Y, Miville-Deschenes, M-A, Stanimirovic, S, Tremblay, CD and van Loon, JT (2022) GASKAP Pilot Survey Science. II. ASKAP Zoom Observations of Galactic 21 cm Absorption. Astrophysical Journal, 926 (2). ISSN 0004-637X

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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°. 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 super-thin 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 the Galactic radius. The ratio of the emission brightness temperature to the absorption, i.e., 1 − e−τ, 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 H i mass.

Item Type: Article
Additional Information: Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Subjects: Q Science > Q Science (General)
Q Science > QB Astronomy
Q Science > QB Astronomy > QB460 Astrophysics
Q Science > QB Astronomy > QB600 Planets. Planetology
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Depositing User: Symplectic
Date Deposited: 25 Mar 2022 09:51
Last Modified: 20 Apr 2022 14:37
URI: https://eprints.keele.ac.uk/id/eprint/10772

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