题 目：X-ray Spectroscopy of Hot Plasma in and around Galaxies
报告人：Qingde Daniel Wang （王青德 教授）
Department of Astronomy, University of Massachusetts, Amherst, USA
摘 要：Much of the baryon matter in the present universe is believed in the form of diffuse hot plasma in and around galaxies. However, little is so far known about the actual properties of this plasma. I will review recent spectroscopic studies of the plasma, based chiefly on X-ray grating data from Chandra and XMM-Newton. The X-ray absorption line spectroscopy has led to the first characterization of the spatial, thermal, chemical, and kinetic properties of the plasma in our Galaxy. The plasma is concentrated around the Galactic bulge and disk on scales of a few kpc. The column density of the plasma on larger scales appears to be at least an order magnitude smaller, indicating that it may not account for the bulk of the missing baryon matter predicted for the Galactic halo according to the standard cosmology. Similar results have also been obtained for other nearby galaxies. Furthermore, a substantial fraction of diffuse soft X-ray emission observed in nearby galaxies cannot arise from optically-thin thermal plasma and most likely originates in charge exchange at the interface with neutral gas, as indicated by the strong forbidden lines of the Kalpha triplets of He-like ions. In general, the bulk of the mass, energy, and metals from the stellar feedback is likely gone with winds in the galaxies. These galactic winds can have profound effects on the galactic ecosystem and evolution.
时 间：2011年11月9日（星期三） 下午2:00
地 点：紫金山天文台 327教室