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首页> 外文期刊>The Astrophysical journal >TRACING THE WARM-HOT INTERGALACTIC MEDIUM AT LOW REDSHIFT: X-RAY FOREST OBSERVATIONS TOWARD H1821+643
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TRACING THE WARM-HOT INTERGALACTIC MEDIUM AT LOW REDSHIFT: X-RAY FOREST OBSERVATIONS TOWARD H1821+643

机译：以低漂移追踪暖热的星际间介质：对H1821 + 643的X射线森林观测

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摘要

We present a high-resolution (λ/Δλ ≈ 500) X-ray spectrum of the bright quasar H1821+643 (z = 0.297), obtained in a 470 ks observation with the Chandra X-Ray Observatory. We search for X-ray absorption by highly ionized metal species, O Ⅶ and O ? in particular, at the redshifts of the six intervening O Ⅵ absorption systems known from UV studies. We detect features with approx>2 σ significance at the predicted O Ⅶ and O Ⅷ wavelengths of one O Ⅵ system, at the O Ⅶ wavelength of a second, and at the Ne Ⅸ wavelength of a third. We find two additional features of comparable strength (one O Ⅶ and one O Ⅷ) within 1000 km s~(-1) of the O Ⅵ redshifts. The 1 σ constraints on the relative abundances of different species imply significant variations from system to system in f(O Ⅵ), the fraction of oxygen in the O Ⅵ state. The constraints in the two detected O Ⅵ systems imply gas overdensities lower than the values δapprox> 100 expected in virialized systems, suggesting that the absorption arises in lower density, filamentary structures. At the 2 σ level, however, the physical constraints are weak, although all of the systems must have temperature T < 10~6 K to be consistent with upper limits on O Ⅷ. If we treat our 2 σ detections of known O Ⅵ systems as real, but assume minimal O Ⅶ and O Ⅷ in the other systems, we estimate [f(O Ⅵ) +f(O Ⅶ) +f(O Ⅷ)]/f(O Ⅵ) = 32 +- 9 for the average ratio of all highly ionized oxygen species to O Ⅵ. Combined with estimates of the total column density of O Ⅵ absorption per unit redshift, this ratio implies that the total baryon fraction associated with detected O Ⅵ absorbers is Ω_b(O Ⅵ) ～ 0.03 h_(70)~(-1), a substantial fraction of the baryon density predicted by big bang nucleosynthesis and larger than that associated with stars or with gas detected in 21 cm or X-ray emission. Because of the limited signal-to-noise ratio of the detections, these results must be treated with caution. Nonetheless, the combination of the O Ⅵ data with these X-ray forest measurements provides the most direct evidence to date for the pervasive, moderate-density, shock-heated intergalactic medium predicted by leading cosmological scenarios. The high inferred incidence of relatively strong O Ⅶ and O Ⅷ absorption implies that some regions of the intergalactic medium are enriched to a level substantially above [O/H] = ―1.
机译：我们展示了明亮的类星体H1821 + 643（z = 0.297）的高分辨率（λ/Δλ≈500）X射线光谱，该光谱是在钱德拉X射线天文台进行的470 ks观测中获得的。我们寻找高离子化金属物种OⅦ和O X的X射线吸收能力吗？特别是在紫外线研究中已知的六个中间OⅥ吸收系统的红移处。我们在一个OⅥ系统的预测OⅦ和OⅧ波长，第二个OⅦ波长和第三个NeⅨ波长处检测到具有大约> 2σ显着性的特征。我们在OⅥ红移的1000 km s〜（-1）范围内发现了两个强度相当的附加特征（一个OⅦ和一个OⅧ）。 1σ约束不同物种的相对丰度意味着f（OⅥ）中各体系之间的显着变化，即fⅥ状态下的氧含量。在两个检测到的OⅥ系统中的约束条件表明气体的密度低于在虚拟化系统中预期的δ大约100。这表明吸收发生在密度较低的丝状结构中。但是，在2σ级别，物理约束较弱，尽管所有系统的温度都必须T <10〜6 K才能与O upper的上限保持一致。如果我们将已知OⅥ系统的2σ检测视为真实，但假设其他系统中的OⅦ和O minimal最小，则我们估计[f（OⅥ）+ f（OⅦ）+ f（OⅧ）] /对于所有高度电离的氧物种与OⅥ的平均比率，f（OⅥ）= 32 +-9。结合每单位红移对OⅥ吸收的总柱密度的估计，该比率意味着与检测到的OⅥ吸收剂相关的总重子分数为Ω_b（OⅥ）〜0.03 h_（70）〜（-1），大爆炸核合成预测的重子密度的分数，大于与恒星或21 cm或X射线探测到的气体有关的重子密度。由于检测的信噪比有限，因此必须谨慎对待这些结果。尽管如此，OⅥ数据与这些X射线森林测量结果的结合为迄今为止由主要宇宙学情景所预测的普遍，中等密度，冲击加热的星系间媒介提供了最直接的证据。较高的OⅦ和OⅧ吸收相对较高的推断发生率意味着银河系中间介质的某些区域富集到实质上高于[O / H] = -1的水平。

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