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ABSTRACT The number of baryons detected in the low-redshift (_z_ < 1) Universe is far smaller than the number detected in corresponding volumes at higher redshifts. Simulations1,2,3 of

the formation of structure in the Universe show that up to two-thirds of the ‘missing’ baryons may have escaped detection because of their high temperature and low density. One of the few

ways to detect this matter directly is to look for its signature in the form of ultraviolet absorption lines in the spectra of background sources such as quasars. Here we show that the

amplitude of the average velocity vector of ‘high velocity’ O vi (O5+) absorption clouds detected in a survey4 of ultraviolet emission from active galactic nuclei decreases significantly

when the vector is transformed to the frames of the Galactic Standard of Rest and the Local Group of galaxies. At least 82 per cent of these absorbers are not associated with any ‘high

velocity’ atomic hydrogen complex in our Galaxy, and are therefore likely to result from a primordial warm–hot intergalactic medium pervading an extended corona around the Milky Way or the

Local Group. The total mass of baryons in this medium is estimated to be up to ∼1012 solar masses, which is of the order of the mass required5 to dynamically stabilize the Local Group.

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support SIMILAR CONTENT BEING VIEWED BY OTHERS THE ACCRETION OF A SOLAR MASS PER DAY BY A 17-BILLION SOLAR MASS BLACK HOLE Article 19 February 2024 H I 21-CENTIMETRE EMISSION FROM AN

ENSEMBLE OF GALAXIES AT AN AVERAGE REDSHIFT OF ONE Article 14 October 2020 ACCELERATED FORMATION OF ULTRA-MASSIVE GALAXIES IN THE FIRST BILLION YEARS  Article 13 November 2024 REFERENCES *

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the OMC-1 peak 1. _Astrophys. J._ (submitted) Download references ACKNOWLEDGEMENTS F.N. thanks P. Kaaret and G. C. Perola for discussions and comments. We thank W.B. Burton for comments that

helped improve the Letter. This work was partly supported by NASA-Chandra grants and a NASA-Chandra X-ray Center contract. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Harvard-Smithsonian

Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts, 02138, USA Fabrizio Nicastro, Andreas Zezas, Martin Elvis, Cesare Cecchi-Pestellini, Douglas Burke, Jeremy Drake & 

Piergiorgio Casella * Astronomy Department, The Ohio State University, Columbus, Ohio, 43210, USA Smita Mathur * Osservatorio Astronomico di Monteporzio, Via Osservatorio Via Frascati 33,

Monteporzio-Catone (RM), I-00040, Italy Fabrizio Fiore Authors * Fabrizio Nicastro View author publications You can also search for this author inPubMed Google Scholar * Andreas Zezas View

author publications You can also search for this author inPubMed Google Scholar * Martin Elvis View author publications You can also search for this author inPubMed Google Scholar * Smita

Mathur View author publications You can also search for this author inPubMed Google Scholar * Fabrizio Fiore View author publications You can also search for this author inPubMed Google

Scholar * Cesare Cecchi-Pestellini View author publications You can also search for this author inPubMed Google Scholar * Douglas Burke View author publications You can also search for this

author inPubMed Google Scholar * Jeremy Drake View author publications You can also search for this author inPubMed Google Scholar * Piergiorgio Casella View author publications You can also

search for this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to Fabrizio Nicastro. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare that they have no

competing financial interests. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Nicastro, F., Zezas, A., Elvis, M. _et al._ The far-ultraviolet signature

of the ‘missing’ baryons in the Local Group of galaxies. _Nature_ 421, 719–721 (2003). https://doi.org/10.1038/nature01369 Download citation * Received: 16 May 2002 * Accepted: 13 December

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