High Resolution X-ray Absorption Line Spectroscopy of the Hot ISM
Abstract
Though the existence of the Galactic hot gas has long been theorized, we still have very limited knowledge of the thermal and chemical properties,
ionization states, and the spatial distribution of this hot medium. The grating instruments aboard Chandra and XMM-Newton X-ray observatories have enabled us for the first time to study the gas properties via high resolution X-ray absorption line spectroscopy. Here I review our recent progress in this field. The OVII, OVIII, and NeIX K shell transition lines have been detected in the spectra of several extragalactic and many Galactic sources, indicating the temperature of the absorbing gas about 10^6 K. A global characterization suggests that the hot gas is concentrated within several kpc distance around the Galactic center region and/or the Galactic disk plane, and that there is significant hot gas absorption beyond the distance of LMC. A detail study of the hot gas toward the sigh line of NGC 6624 (4U 1820-303) gives Ne/O abundance ratio about 1 solar and the hot gas filling factor about unit. Modeling the detected FeXVII absorption line in this sigh line also leads us to conclude that iron is only mildly depleted onto dust grain in hot medium, consistent with theoretical suggestion that the dust grain could be destructed in the shock-heating process. This work has been supported by NASA through SAO contract to MIT for support of the Chandra CXC.- Publication:
-
AAS/High Energy Astrophysics Division #9
- Pub Date:
- September 2006
- Bibcode:
- 2006HEAD....9.0118Y