Global Distribution of Far-ultraviolet Emissions from Highly Ionized Gas in the Milky Way

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We present all-sky maps of two major far-ultraviolet cooling lines, C IV and O VI, of highly ionized gas to investigate the nature of the transition-temperature gas. From the extinction-corrected line intensities of C IV and O VI, we calculated the gas temperature and the emission measure of the transition-temperature gas assuming isothermal plasma in the collisional ionization equilibrium. The gas temperature was found to be more or less uniform throughout the Galaxy with a value of (1.89 +/- 0.06) x 10(5) K. The emission measure of the transition-temperature gas is described well by a disk-like model in which the scale height of the electron density is z(0) = 6(-2)(+3) kpc. The total mass of the transition-temperature gas is estimated to be approximately 6.4(-2.8)(+5.2) x 10(9)M(circle dot). We also calculated the volume-filling fraction of the transition-temperature gas, which was estimated to be f = 0.26 +/- 0.09, and it varies from f similar to 0.37 in the inner Galaxy to f similar to 0.18 in the outer Galaxy. The spatial distribution of C IV and O VI cannot be explained by a simple supernova remnant model or a three-phase model. The combined effects of supernova remnants and turbulent mixing layers can explain the intensity ratio of C IV and O VI. Thermal conduction front models and high-velocity cloud models are also consistent with our observation.
Publisher
IOP PUBLISHING LTD
Issue Date
2019-07
Language
English
Article Type
Article
Citation

ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, v.243, no.1, pp.9

ISSN
0067-0049
DOI
10.3847/1538-4365/ab22ae
URI
http://hdl.handle.net/10203/263736
Appears in Collection
PH-Journal Papers(저널논문)
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