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外文期刊>The Astrophysical journal
>A New Measurement of the Primordial Abundance of Deuterium: Toward Convergence with the Baryon Density from the Cosmic Microwave Background?*
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A New Measurement of the Primordial Abundance of Deuterium: Toward Convergence with the Baryon Density from the Cosmic Microwave Background?*
From the analysis of the near-UV spectrum of the quasar (QSO)2206-199, obtained with a long series of exposures with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we deduce a value D/H = (1.65 ± 0.35) × 10-5 (1 σ error) for the abundance of deuterium in the zabs = 2.0762 damped Lyα system (DLA) along this sight line. The velocity structure of this absorber is very simple, and its neutral hydrogen column density N(H I) is accurately known; the error in D/H is mostly due to the limited signal-to-noise ratio of the spectrum. Since this is also one of the most metal-poor DLAs, with metal abundances ~1/200 of solar, the correction due to the astration of D is expected to be insignificant, and the value we deduce should be essentially the primordial abundance of deuterium. When all (six) available measurements of D/H in high-redshift QSO absorbers are considered, we find that the three DLAs, N(H I) is measured most reliably, give consistently lower values than the three Lyman limit systems. We point out that the weighted mean of the DLA measurements, D/H = (2.2 ± 0.2) × 10-5, yields a baryon density ΩBh2 = 0.025 ± 0.001, which is within ~1 σ of the value deduced from the analysis of the cosmic microwave background angular power spectrum, and is still consistent with the present-day D/H and models of Galactic chemical evolution. Future observations of D I absorption in other DLAs are needed to establish whether our finding reflects a real advantage of DLAs over other classes of QSO absorbers for the measurement of D or if it is just a statistical fluctuation.
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机译：通过对类星体（QSO）2206-199的近紫外光谱的分析（通过在哈勃太空望远镜上使用太空望远镜成像光谱仪进行的长时间曝光获得的）得出了D / H =（1.65±0.35） ）×10-5（1σ误差），表示沿视线的zabs中的氘丰度= 2.0762阻尼Lyα系统（DLA）。该吸收器的速度结构非常简单，其中性氢柱密度N（H I）准确已知。 D / H的误差主要是由于频谱的信噪比有限。由于这也是金属贫乏的DLA之一，太阳能的金属丰度约为1/200，因此，由于D的误位而引起的校正预计微不足道，我们得出的值基本上应该是氘的原始丰度。当考虑所有（六个）高红移QSO吸收器中D / H的测量值时，我们发现三个DLA（N（HI））的测量最为可靠，其值始终低于三个Lyman极限系统。我们指出DLA测量的加权平均值D / H =（2.2±0.2）×10-5，得出的重子密度ΩBh2= 0.025±0.001，在从分析得出的值的〜1σ之内宇宙微波背景角功率谱，并且仍然与当今的D / H和银河化学演化模型一致。还需要对其他DLA中D I吸收的未来观察来确定我们的发现是否反映了DLA相对于其他QSO吸收剂类别在D测量方面的真正优势，还是仅仅是统计上的波动。
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