A quasar reddened by a sub-parsec-sized, metal-rich and dusty cloud in a damped Lyman α absorber at z = 2.13
A quasar reddened by a sub-parsec-sized, metal-rich and dusty cloud in a damped Lyman α absorber at z = 2.13
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类星体在 z = 2.13 处的阻尼莱曼 α 吸收器中被亚秒差距大小、富含金属和尘埃的云变红
DOI：
10.1093/mnras/stv2346
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发表时间：
2015
影响因子：
4.8
通讯作者：
A. Stockton
中科院分区：
文献类型：
--
作者：
J. Krogager;J. Krogager;J. Fynbo;P. Noterdaeme;T. Zafar;P. Møller;C. Ledoux;T. Krühler;A. Stockton
我们对 z=2.32 处的红色类星体以及 z=2.13 处介入的阻尼莱曼-α 吸收体 (DLA) 进行了详细分析。利用 ESO 甚大望远镜 X 射手摄谱仪的高质量数据，我们发现吸收体的金属丰度与太阳一致。我们观察到强烈的 C I 和 H$_2$ 吸收，表明存在冷、致密的吸收介质。在 C I 线中观察到部分覆盖效应，从中我们推断出覆盖分数为 $27 \pm 6$ %，云的物理直径为 0.1 pc。根据覆盖分数和大小，我们估计背景类星体的宽线区域的大小。我们在光学和近红外成像中寻找 DLA 对应物的发射。在光学数据中没有观察到发射。然而，我们在 H 和 K' 波段图像中看到了对应物的初步证据。 DLA 显示出高损耗（通过 [Fe/Zn]=-1.22 探测），表明 DLA 中必定存在大量灰尘。通过用各种尘埃红化类星体模板拟合光谱，我们发现 DLA 中尘埃的最佳拟合量为 $A(V)_{\rm DLA}=0.28 \pm 0.01|_{\rm stat} \pm 0.07|_{\rm sys}$。我们得出的结论是，DLA 中的尘埃导致这个本质上非常明亮的背景类星体的颜色看起来比普通类星体红得多，从而不符合斯隆数字巡天中类星体识别的标准。因此，这种化学富集和多尘的吸收剂在当前的 DLA 样品中代表性不足。
We present a detailed analysis of a red quasar at z=2.32 with an intervening damped Lyman-alpha absorber (DLA) at z=2.13. Using high quality data from the X-shooter spectrograph at ESO Very Large Telescope we find that the absorber has a metallicity consistent with Solar. We observe strong C I and H$_2$ absorption indicating a cold, dense absorbing medium. Partial coverage effects are observed in the C I lines, from which we infer a covering fraction of $27 \pm 6$ % and a physical diameter of the cloud of 0.1 pc. From the covering fraction and size, we estimate the size of the background quasar's broad line region. We search for emission from the DLA counterpart in optical and near-infrared imaging. No emission is observed in the optical data. However, we see tentative evidence for a counterpart in the H and K' band images. The DLA shows high depletion (as probed by [Fe/Zn]=-1.22) indicating that significant amounts of dust must be present in the DLA. By fitting the spectrum with various dust reddened quasar templates we find a best-fitting amount of dust in the DLA of $A(V)_{\rm DLA}=0.28 \pm 0.01|_{\rm stat} \pm 0.07|_{\rm sys}$. We conclude that dust in the DLA is causing the colours of this intrinsically very luminous background quasar to appear much redder than average quasars, thereby not fulfilling the criteria for quasar identification in the Sloan Digital Sky Survey. Such chemically enriched and dusty absorbers are thus underrepresented in current samples of DLAs.