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E. Lloyd-Davies, J. Bregman (University of Michigan)
The star formation history of the galaxy has left a substantial imprint on the interstellar medium in the form pollution from metals generated by supernovae. The abundance of metals in the ISM is therefore an extremely important probe of past supernova activity. Optical measurements of the metal abundance in the ISM can be uncertain due to corrections for ionization and dust. However absorption at X-ray wavelengths is relatively insensitive to these effects, in principle allowing much greater accuracy.
We present the analysis of ISM absorption in XMM-Newton Reflection Grating Spectrometer observations of a sample of bright AGN. We determine a median O abundance of ~0.6 solar and a median Fe abundance of ~1 solar with evidence for intrinsic variation in abundance along different sight lines. We obtain Fe/O abundance ratios of 2-3 and comment on the implication of these results for models of the star formation history in the Milky Way. We acknowledge the support of NASA for this project.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.