A Galactic Origin for the Local Ionized X-ray Absorbers
  Recent Chandra and XMM 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 archival data. About 40% of the targets show local OVII He-alpha absorption with column densities around 10^16 cm^-2; in particular, OVII absorption is present in all the high quality spectra. We estimate that the sky covering fraction of this OVII-absorbing gas is at least 63%, at 90% confidence, and likely to be unity given enough high-quality spectra. Based on (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 test of this result. 
Taotao Fang (1), Christopher McKee (1), Claude Canizares (2), Mark   Wolfire (3) ((1) UC Berkeley, (2) MIT, (3) Maryland)