A Galactic Origin for the Local Ionized X-ray Absorbers
Author(s)Fang, Taotao; Mckee, Christopher F.; Canizares, Claude R.; Wolfire, Mark
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Recent Chandra and XMM-Newton observations of distant quasars have shown strong local (z ~ 0) X-ray absorption lines from highly ionized gas, primarily He-like oxygen. The nature of these X-ray absorbers, i.e., whether they are part of the hot gas associated with the Milky Way or part of the intragroup medium in the Local Group, remains a puzzle due to the uncertainties in the distance. We present in this paper a survey of 20 AGNs with Chandra and XMM-Newton archival data. About 40% of the targets show local O VII He α absorption with column densities around 10[superscript 16] cm[superscript -2]; in particular, O VII absorption is present in all the high-quality spectra. We estimate that the sky covering fraction of this O VII-absorbing gas is at least 63%, at 90% confidence, and likely to be unity given enough high-quality spectra. On the basis of (1) the expected number of absorbers along sight lines toward distant AGNs, (2) joint analysis with X-ray emission measurements, and (3) mass estimation, we argue that the observed X-ray absorbers are part of the hot gas associated with our Galaxy. Future observations will significantly improve our understanding of the covering fraction and provide robust tests of this result.
DepartmentMassachusetts Institute of Technology. Department of Physics
Fang, Taotao et al. “A Galactic Origin for the Local Ionized X‐Ray Absorbers.” The Astrophysical Journal 644.1 (2006): 174-179.
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