Files
Abstract
Galactic diffuse hot gas of temperature ~10^6 K that constitutes most of theinterstellar space remains the least well known component of the interstellar medium.We present in this dissertation two studies of the Galactic diffuse hot gas usingshadowing observation and joint analysis methods. We first analyze a pair of Suzakushadowing observations in order to determine the X-ray spectrum of the Galaxy'sgaseous halo. Our X-ray measurements, together with the FUSE OVI and SPEARCIV observations for the same (or nearby) direction, indicate the existence of hot halogas at temperatures of ~10^5 K to ~10^7 K. We construct a broken power-lawdifferential emission measure model for the hot halo gas. We find that a simple modelin which hot gas accretes onto the Galactic halo and cools radioactively cannot explainboth the observed UV and X-ray portions of our broken power-law model. However, theUV and X-ray intensities and our broken power-law model can be well explained by hotgas produced by supernova explosions supplemented by a smooth source of X-rays.We also construct a sample of 19 directions with both OVII emission intensity andabsorption equivalent width measurements made from XMM-Newton archival datafor the study of the Galactic diffuse hot gas. Both the OVII emission and absorptionstrengths are significantly enhanced toward the inner region of the Galaxy, where theGalactic center soft X-ray enhancement (GCSXE) is seen in the ROSAT 3/4 keV map.We find a tight correlation between the OVII absorption equivalent width and the OVIIemission intensity at the 97.9% confidence level for these 19 directions, stronglysuggesting that the OVII emission and absorption are largely co-spatial. Our jointanalyses of the OVII emission and absorption show that the hot gas on the directionsoff the GCSXE are in good agreement with a thick disk model. While for the hot gasassociated with the GCSXE, our results support its Galactic center/bulge origin.We also propose in this dissertation a future study of the hot gas associated with theGCSXE using differential/joint analyses.