Seminar Title:	Galactic Diffuse Hot Gas: Shadowing observations and Joint Analyses
Speaker:	Dr. Shijun Lei
Affiliation:	(Univ. of Georgia, USA)
When:	Wednesday Afternoon, Dec. 22th, 2:30 p.m
Where:	Room 327, Office Block, 2 West Beijing Road (PMO, CAS)
	Welcome to Attend
	( PMO Academic Committee & Academic Circulating committee)

　Abstract　　

　  Million degree hot gas constitutes most of the interstellar space in our Galaxy but remains the least well known component of the interstellar medium. I introduce in this talk two of my studies of the Galactic diffuse hot gas using shadowing observation and joint analysis methods. In the first work we analyze a pair of Suzaku shadowing observations to determine the X-ray spectrum of the Galaxy's gaseous halo. Our soft X-ray measurements, together with the OVI and CIV observations for the same direction, indicate the existence of hot halo gas covering a wide temperature range of ~10^5-10^7 K, whose differential emission measure is found to follow a broken power-law model. We find that a simple model in which hot gas accretee onto the Galactic halo and cools radioactively cannot explain both the observed UV and X-ray portions of our broken power-law model. However, the UV and X-ray intensities can be well explained by hot gas produced by supernova explosions supplemented by a smooth source of X-rays. In the second work we construct a sample of 19 directions with both OVII emission intensity and absorption equivalent width measurements made from XMM-Newton archival data. Both the OVII emission and absorption strengths are significantly enhanced toward the Galactic center soft X-ray enhancement (GCSXE).A tight correlation between the OVII absorption equivalent width and the OVII emission intensity of the 19 directions at the 97.9% confidence level strongly suggests that the OVII emission and absorption are largely co-spatial. Our joint analyses of the OVII emission and absorption show that the hot gas on the directions off the GCSXE is in good agreement with a thick disk model.

While for the hot gas associated with the GCSXE, our results support its Galactic center/bulge origin.