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|Title:||Observations of the missing baryons in the warm-hot intergalactic medium||Authors:||NICASTRO, FABRIZIO
Branchini, Enzo Franco
Danforth, C. W.
Shull, J. M.
|Issue Date:||2018||Journal:||NATURE||Number:||558||Issue:||7710||First Page:||406||Abstract:||It has been known for decades that the observed number of baryons in the local Universe falls about 30-40 per cent short<SUP>1,2</SUP> of the total number of baryons predicted<SUP>3</SUP> by Big Bang nucleosynthesis, as inferred<SUP>4,5</SUP> from density fluctuations of the cosmic microwave background and seen during the first 2-3 billion years of the Universe in the so-called `Lyman α forest'<SUP>6,7</SUP> (a dense series of intervening H i Lyman α absorption lines in the optical spectra of background quasars). A theoretical solution to this paradox locates the missing baryons in the hot and tenuous filamentary gas between galaxies, known as the warm-hot intergalactic medium. However, it is difficult to detect them there because the largest by far constituent of this gas—hydrogen—is mostly ionized and therefore almost invisible in far-ultraviolet spectra with typical signal-to-noise ratios<SUP>8,9</SUP>. Indeed, despite large observational efforts, only a few marginal claims of detection have been made so far<SUP>2,10</SUP>. Here we report observations of two absorbers of highly ionized oxygen (O vii) in the high-signal-to-noise-ratio X-ray spectrum of a quasar at a redshift higher than 0.4. These absorbers show no variability over a two-year timescale and have no associated cold absorption, making the assumption that they originate from the quasar's intrinsic outflow or the host galaxy's interstellar medium implausible. The O vii systems lie in regions characterized by large (four times larger than average<SUP>11</SUP>) galaxy overdensities and their number (down to the sensitivity threshold of our data) agrees well with numerical simulation predictions for the long-sought warm-hot intergalactic medium. We conclude that the missing baryons have been found.||URI:||http://hdl.handle.net/20.500.12386/30746||URL:||https://www.nature.com/articles/s41586-018-0204-1||ISSN:||0028-0836||DOI:||10.1038/s41586-018-0204-1||Bibcode ADS:||2018Natur.558..406N||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Jun 14, 2021
checked on Jun 14, 2021
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