X-RAYING THE INTERGALACTIC O VI ABSORBERS
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Author(s)
Yao, Y.
Tripp, T. M.
Wang, Q. D.
Danforth, Charles W.
Canizares, Claude R.
Shull, J. M.
Song, L.
Marshall, Herman
Date Issued
May 2009
Journal
Astrophysical Journal
Publisher
American Astronomical Society
Citation
X-raying the Intergalactic O VI Absorbers
Y. Yao, T. M. Tripp, Q. D. Wang, C. W. Danforth, C. R. Canizares, J. M. Shull, H. L. Marshall, and L. Song 2009 ApJ 697 1784-1792 doi: 10.1088/0004-637X/697/2/1784 (C)2009 The American Astronomical Society.
Version
Final published version
Abstract
The observed intergalactic O vi absorbers at z > 0 have been regarded as a significant reservoir of the “missing
baryons.” However, to fully understand how these absorbers contribute to the baryon inventory, it is crucial to
determine whether the systems are collisionally ionized or photoionized (or both). Using the identified intergalactic
Ovi absorbers as tracers, we search for the corresponding X-ray absorption lines, which are useful for finding
the missing baryons and for revealing the nature of the O vi absorbers. Stacking the Chandra grating spectra
along six AGN sight lines, we obtain three spectra with signal-to-noise ratios of 32, 28, and 10 per 12.5 mÅ
spectral bin around the expected O vii Kα wavelength. These spectra correspond to O vi absorbers with various
dynamic properties. We find no detectable Ne ix, O vii, O viii, N vii, or C vi absorption lines in the spectra, but
the high counting statistics allows us to obtain firm upper limits on the corresponding ionic column densities
(in particular NO vii < 10N [subscript Ovi] on average at the 95% confidence level). Jointly analyzing these nondetected Xray
lines with the averaged O vi column density, we further limit the average temperature of the Ovi-bearing
gas to be T < 10 [superscript 5.7] K in collisional ionization equilibrium. We discuss the implications of these results for
physical properties of the putative warm–hot intergalactic medium and its detection in future X-ray observations.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
http://dx.doi.org/10.1088/0004-637X/697/2/1784
