Hot Gas in the Galactic Thick Disk and Halo Near the Draco Cloud

This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of {approx}10{sup 5} to {approx}3 x 10{...

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Bibliographic Details
Published in:The Astrophysical journal 2010-10, Vol.722 (1), p.302-310, Article 302
Main Authors: Shelton, R. L, Henley, D. B, Dixon, W. V
Format: Article
Language:English
Subjects:
Astronomy
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BOSONS
COOLING
EARTH PLANET
Earth, ocean, space
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ENERGY TRANSFER
Exact sciences and technology
GALAXIES
HEAT TRANSFER
IONIZING RADIATIONS
MASSLESS PARTICLES
NORTHERN HEMISPHERE
PHOTONS
PHYSICS
PLANETS
RADIATIONS
RADIATIVE COOLING
THERMAL CONDUCTION
ULTRAVIOLET RADIATION
X RADIATION
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Summary:This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of {approx}10{sup 5} to {approx}3 x 10{sup 6} K. We measured the O VI, O VII, and O VIII intensities from FUSE and XMM-Newton data and subtracted off the local contributions in order to deduce the thick disk/halo contributions. These were supplemented with published C IV intensity and O VI column density measurements. Our estimate of the thermal pressure in the O VI-rich thick disk/halo gas, p{sub th}/k = 6500{sup +2500}{sub -2600} K cm{sup -3}, suggests that the thick disk/halo is more highly pressurized than would be expected from theoretical analyses. The ratios of C IV to O VI to O VII to O VIII intensities were compared with those predicted by theoretical models. Gas which was heated to 3 x 10{sup 6} K then allowed to cool radiatively cannot produce enough C IV or O VI-generated photons per O VII or O VIII-generated photon. Producing enough C IV and O VI emission requires heating additional gas to 10{sup 5} K < T < 10{sup 6} K. However, shock heating, which provides heating across this temperature range, overproduces O VI relative to the others. Obtaining the observed mix may require a combination of several processes, including some amount of shock heating, heat conduction, and mixing, as well as radiative cooling of very hot gas.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/722/1/302