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Observations of the missing baryons in the warm- hot intergalactic medium

机译：在银热星际介质中缺失的重子的观测

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摘要

It has been known for decades that the observed number of baryons in the local Universe falls about 30-40 per cent short(1,2) of the total number of baryons predicted(3) by Big Bang nucleosynthesis, as inferred(4,5) 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 alpha forest'(6,7) (a dense series of intervening H I Lyman alpha 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(8,9). Indeed, despite large observational efforts, only a few marginal claims of detection have been made so fat(2,10). 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(11)) 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.
机译：几十年来，已知在宇宙中观察到的重子数目比大爆炸核合成预测的重子总数（3）短约30-40％（1,2），据推断（4,5 ）从宇宙微波背景的密度波动中，以及在宇宙的前2-3亿年在所谓的``莱曼阿尔法森林''（6,7）中看到的（密集的一系列介入的莱曼阿尔法吸收线类星体的光谱）。对这一悖论的理论解决方案是将缺失的重子定位在星系之间的热而微弱的丝状气体中，这被称为“热-热星系间介质”。但是，很难在那儿检测到它们，因为这种气体氢中到目前为止最大的成分大部分已被电离，因此在具有典型信噪比的远紫外光谱中几乎看不见（8,9）。的确，尽管付出了巨大的观察努力，但只有很少的检测要求如此胖（2,10）。在这里，我们报道了类星体在红移高于0.4时在高信号噪声比X射线光谱中观察到的两种高度电离的氧气（O VII）吸收剂。这些吸收剂在两年的时间范围内没有变化，也没有相关的冷吸收，因此假设它们来自类星体的固有流出或宿主星系的星际介质是不可信的。 O VII系统位于以大（超过平均值（11）的四倍大）为特征的区域，其数目（下降到我们数据的敏感度阈值）与长期寻找的温暖热星际介质的数值模拟预测非常吻合。我们得出结论，发现了缺失的重子。

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  • 来源
    《Nature》 |2018年第7710期|406-409|共4页
  • 作者

    Nicastro F.; Kaastra J.; Krongold Y.; Borgani S.; Branchini E.; Cen R.; Dadina M.; Danforth C. W.; Elvis M.; Fiore F.; Gupta A.; Mathur S.; Mayya D.; Paerels F.; Piro L.; Rosa-Gonzalez D.; Schaye J.; Shull J. M.; Torres-Zafra J.; Wijers N.; Zappacosta L.;

  • 作者单位

    Ist Nazl Astrofis INAF, Osservatorio Astron Roma, Rome, Italy;

    SRON Netherlands Inst Space Res, Utrecht, Netherlands;

    Univ Nacl Autonoma Mexico, Inst Astron, Mexico City, DF, Mexico;

    Univ Trieste, Phys Dept, Trieste, Italy;

    Univ Roma Tre, Phys Dept, Rome, Italy;

    Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA;

    INAF, Osservatorio Astrofis Sci Spazio Bologna, Bologna, Italy;

    Univ Colorado, Dept Astrophys Sci, Boulder, CO 80309 USA;

    Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02138 USA;

    Ist Nazl Astrofis INAF, Osservatorio Astron Roma, Rome, Italy;

    Columbus State Community Coll, Columbus, OH USA;

    Ohio State Univ, Columbus, OH USA;

    Inst Nacl Astrofis Opt & Electr, Puebla, Mexico;

    Columbia Univ, Dept Astron, New York, NY 10027 USA;

    INAF, Ist Astrofis & Planetol Spaziali, Rome, Italy;

    Leiden Observ, Leiden, Netherlands;

    Univ Colorado, Dept Astrophys Sci, Boulder, CO 80309 USA;

    UNLP, IALP, La Plata, Buenos Aires, Argentina;

    Leiden Observ, Leiden, Netherlands;

    Ist Nazl Astrofis INAF, Osservatorio Astron Roma, Rome, Italy;

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