Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.305p&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Astronomy and Astrophysics
Astronomy
Scientific paper
The interstellar medium (ISM) has a multiphase structure characterized by gas, dust and molecules. The interstellar gas consists of different charge states: neutral, weakly-ionized and highly-ionized. Dust is mainly found in carbonaceous and silicates compounds, and molecules like CO and CH are also common. Through the study of the X-ray absorption lines in the spectra of background sources it is possible to probe the different phases of the interstellar medium of our Galaxy and to estimate the abundances of the most abundant elements, such as oxygen, iron, and neon. We present our results on high-quality spectra taken with the Reflection Grating Spectrometer onboard XMM-Newton along different lines of sight with a detailed analysis of the absorption features due to the neutral and ionized gas of the ISM, as well as absorption by dust. We find significant deviations from Solar abundances, especially when the line of sight points towards the inner regions of the Galaxy. Towards the innermost regions the abundances exceed the Solar values in agreement with the metallicity gradient measured at longer wavelengths. The bulk of the interstellar gas is neutral, but a significant fraction of the interstellar matter is found in dust grains. We show how the fine structure of the absorption edges contains clues on the chemical composition of the dust grains. For instance, most of the solid oxygen is found in silicates compounds of pyroxene MgSiO3.
Costantini Elisa
Kaastra Jelle S.
Pinto Cecilia
Verbunt Frank
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