HOT GAS IN THE GALACTIC THICK DISK AND HALO NEAR THE DRACO CLOUD

Journal Article · Sun Oct 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/1/302· OSTI ID:21464701

Shelton, R L; Henley, D B ^[1]

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1. Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

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.

• OSTI ID: 21464701
• Journal Information: Astrophysical Journal, Vol. 722, Issue 1; Other Information: DOI: 10.1088/0004-637X/722/1/302; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
GALAXIES
NORTHERN HEMISPHERE
PHOTONS
RADIATIVE COOLING
THERMAL CONDUCTION
ULTRAVIOLET RADIATION
X RADIATION
BOSONS
COOLING
EARTH PLANET
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ENERGY TRANSFER
HEAT TRANSFER
IONIZING RADIATIONS
MASSLESS PARTICLES
PHYSICS
PLANETS
RADIATIONS