Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...208.3704s&link_type=abstract
American Astronomical Society Meeting 208, #37.04; Bulletin of the American Astronomical Society, Vol. 38, p.113
Astronomy and Astrophysics
Astronomy
Scientific paper
Since the Copernicus mission, we have known that highly ionized gas exists above the Galactic plane. ROSAT shadowing observations show that X-ray emitting gas resides above the plane, as well. The observations challenge us to determine this plasma's sources, properties, and effects. Is the gas as hot as its equilibrium ionization temperature implies (300,000 to 1,000,000 K), or cooler and out of equilibrium? Could this plasma trace a circulating flow between the disk and halo, or, conversely, was the plasma heated and ionized by energy sources located above the Galactic disk? One energy source is supernova explosions. The distribution of isolated supernova progenitor stars extends hundreds of parsecs above the disk. The higher explosions are rarer, but produce longer lived supernova remnant bubbles. In addition, the interiors of the old bubbles may possibly be buoyant relative to their surroundings. By coupling computer simulation results with analytic calculations of buoyancy, it has been possible to estimate the quantity, distribution, kinematics, and physical properties of the hot gas in extra-planar supernova remnants. Irrespective of the assumed buoyant drag and supernova explosion energy, the predicted O VI column density as a function of height above the plane for the population of extra-planar supernova remnants matches the observed distribution between 130 pc (the size scale of the Local Bubble) and 2000 pc. The predicted surface brightness of 1/4 keV X-rays ranges up to 320 x 10^{-6} ROSAT 1/4 keV counts/s/arcmin^2, explaining most of the emission attributed to the halo in the Milky Way's southern hemisphere. Such comparisons indicate that isolated supernova remnants are important contributers to the halo's hot gas content. In this talk, I will discuss these comparisons as well as comparisons between observations and the plasma's predicted maximum buoyant rise, velocity distribution, spatial distribution, and physical conditions.
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