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The mass of the missing baryons in the X-ray forest of the warm–hot intergalactic medium

Abstract

Recent cosmological measurements indicate that baryons comprise about four per cent of the total mass-energy density of the Universe1,2, which is in accord with the predictions arising from studies of the production of the lightest elements3. It is also in agreement with the actual number of baryons detected at early times (redshifts z > 2)4,5. Close to our own epoch (z < 2), however, the number of baryons detected add up to just over half ( 55 per cent) of the number seen at z > 2 (refs 6–11), meaning that about 45 per cent are ‘missing’. Here we report a determination of the mass-density of a previously undetected population of baryons, in the warm–hot phase of the intergalactic medium. We show that this mass density is consistent, within the uncertainties, with the mass density of the missing baryons.

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Figure 1: The WHIM absorption in the Chandra LETG spectrum of Mkn 421.
Figure 2: The ‘missing’ baryons have been found in the WHIM.

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Acknowledgements

This work has been supported in part by NASA-Chandra and NASA-LTSA grants.

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Correspondence to Fabrizio Nicastro.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Methods

(a) Observations. (b) Data Reduction and Analysis. (c) Comparison of Data with Models. (DOC 49 kb)

Supplementary Discussion

(a) Line Identification: ruling out blazar outflows. (b) Metallicity dependency on modeling. (DOC 44 kb)

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Nicastro, F., Mathur, S., Elvis, M. et al. The mass of the missing baryons in the X-ray forest of the warm–hot intergalactic medium. Nature 433, 495–498 (2005). https://doi.org/10.1038/nature03245

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  • DOI: https://doi.org/10.1038/nature03245

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