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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Bennett, C. L. et al. First-year Wilkinson microwave anisotropy probe (WMAP) observations: preliminary maps and basic results. Astrophys. J. Suppl. 148, 1–27 (2003)
Spergel, D. N. et al. First-year Wilkinson microwave anisotropy probe (WMAP) observations: determination of cosmological parameters. Astrophys. J. Suppl. 148, 175–194 (2003)
Kirkman, D., Tytler, D., Suzuki, M., O'Meara, J. M. & Lubin, D. The cosmological baryon density from the deuterium-to-hydrogen ratio in QSO absorption systems: D/H toward Q1243 + 3047. Astrophys. J. Suppl. 149, 1–28 (2003)
Rauch, M. The Lyman Alpha forest in the spectra of QSOs. Annu. Rev. Astron. Astrophys. 36, 267–316 (1998)
Weinberg, D. H., Miralda-Escude, J., Hernquist, L. & Katz, N. A lower bound on the cosmic baryon density. Astrophys. J. 490, 564–570 (1997)
Fukugita, M. Cosmic matter distribution: cosmic baryon budget revisited. In Dark Matter in Galaxies (Proc. IAU Symp. 220, in the press); preprint at http://www.arXiv.org/astro-ph/0312517 (2003)
Shull, J. M. in The IGM/Galaxy Connection (eds Rosenberg, J. L. & Putman, M. E.) Vol. 281, 1–10 (Kluwer Academic, Dordrecht, 2003)
Stocke, J. T., Shull, J. M. & Penton, S. V. The baryon content of the local intergalactic medium. Proc. 2004 STScI May Symp. on Planets to Cosmology: Essential Science in Hubble's Final Years (Cambridge Univ. Press, in the press); preprint at http://www.arXiv.org/astro-ph/0407352 (2004)
Penton, S. V., Stocke, J. T. & Shull, J. M. The local Lyα forest. IV. Space Telescope Imaging Spectrograph G140M spectra and results on the distribution and baryon content of HI absorbers. Astrophys. J. Suppl. 152, 29–62 (2004)
Tripp, T. M., Savage, B. D. & Jenkins, E. B. Intervening O VI quasar absorption systems at low redshift: a significant baryon reservoir. Astrophys. J. 534, L1–L5 (2000)
Savage, B. D., Sembach, K. R., Tripp, T. M. & Richter, P. Far ultraviolet spectroscopic explorer and Space Telescope Imaging Spectrograph observations of intervening O VI absorption line systems in the spectrum of PG 0953 + 415. Astrophys. J. 564, 631–649 (2002)
Cen, R. & Ostriker, J. P. Where are the baryons? Astrophys. J. 514, 1–6 (1999)
Davé, R. et al. Baryons in the warm-hot intergalactic medium. Astrophys. J. 552, 473–483 (2001)
Fang, T., Bryan, G. L. & Canizares, C. R. Simulating the X-ray forest. Astrophys. J. 564, 604–623 (2002)
Perna, R. & Loeb, A. X-ray absorption by the hot intergalactic medium. Astrophys. J. 503, L135–L138 (1998)
Nicastro, F. et al. The far-ultraviolet signature of the ‘missing’ baryons in the Local Group of galaxies. Nature 421, 719–721 (2003)
Sembach, K. R. et al. Highly ionized high-velocity gas in the vicinity of the galaxy. Astrophys. J. Suppl. 146, 165–208 (2003)
Collins, J. A., Shull, J. M. & Giroux, M. L. Highly ionized high-velocity clouds toward PKS 2155–304 and Markarian 509. Astrophys. J. 605, 216–229 (2004)
Nicastro, F. et al. Chandra discovery of a tree in the X-ray forest toward PKS 2155–304: The local filament? Astrophys. J. 573, 157–167 (2002)
Fang, T., Sembach, K. R. & Canizares, C. R. Chandra detection of local O VII Heα absorption along the sight line toward 3C 273. Astrophys. J. 586, L49–L52 (2003)
Rasmussen, A., Kahn, S. M. & Paerels, F. X-ray IGM in the Local Group, The IGM/Galaxy Connection (eds Rosenberg, J. L. & Putman, M. E.) 109–115 (Kluwer Academic, Dordrecht, 2003)
Cagnoni, I., Nicastro, F., Maraschi, L., Treves, A. & Tavecchio, F. A view of PKS 2155–304 with XMM-Newton reflection grating spectrometers. Astrophys. J. 603, 449–455 (2004)
Nicastro, F. in Chandra and FUSE View of the WHIM: The Local Group and Beyond, Maps of the Cosmos (14–17 July 2003, Sydney, Australia) (eds Colless, M. & Staveley-Smith, L.) 170–177 (International Astronomical Union Symp. 216, IAU, 2003)
Shull, J. M., Stocke, J. T. & Penton, S. Intergalactic hydrogen clouds at low redshift: connections to voids and dwarf galaxies. Astron. J. 111, 72–77 (1996)
Mathur, S., Weinberg, D. H. & Chen, X. Tracing the warm-hot intergalactic medium at low redshift: X-ray forest observations toward H1821 + 643. Astrophys. J. 582, 82–94 (2003)
Fang, T., Marshall, H. L., Lee, J. C., Davis, D. S. & Canizares, C. R. Chandra detection of O VIII Lyα absorption from an overdense region in the intergalactic medium. Astrophys. J. 572, L127–L130 (2002)
Savage, B. D., Sembach, K. R., Tripp, T. M. & Richter, P. Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph observations of intervening O VI absorption line systems in the spectrum of PG 0953 + 415. Astrophys. J. 564, 631–649 (2002)
Gehrels, N. Confidence limits for small numbers of events in astrophysical data. Astrophys. J. 303, 336–346 (1986)
This work has been supported in part by NASA-Chandra and NASA-LTSA grants.
The authors declare that they have no competing financial interests.
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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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