高红移AGN中的冷中性气体在哪里？
Where is the Cold Neutral Gas in the Hosts of High Redshift AGN?
摘要：
在z > 0.1的射电星系和类星体中，对HI 21-cm吸收的先前观测产生了40%的探测率，这归因于活动星系核（AGN）的统一方案。在这个范例中，吸收仅在（接近）2型物体中被观察到，其中中心遮蔽被（几乎）边缘观察到，因此沿着我们的视线吸收了其余帧1420 MHz发射。然而，我们发现这种探测和未探测的混合只适用于低红移（z < 1）：从对8个z > 3射电源的敏感调查中，我们没有发现21厘米的吸收，这表明这些物体中（搜索的视线）冷中性气体的丰度很低。分析这些源的光谱能量分布，我们发现，我们的高红移的选择引入了一个偏见，我们的样本完全由类星体的紫外线光度超过10 e23 W/Hz。这可能表明我们已经选择了一类特别紫外线明亮的1型物体。无论原因是什么，它也必须被用来解释在相同数量的z < 0.7源中的未检测，其中我们第一次发现在> 10 e23 W/Hz时相同的排他性未检测。这些物体也被证明是类星体，从这些独特的高紫外光度-21厘米的非检测，很明显，方向效应本身不能解释在任何红移的21厘米检测和非检测的混合。
英文摘要：
Previous surveys for HI 21-cm absorption in z > 0.1 radio galaxies and quasars yield a 40% detection rate, which is attributed to unified schemes of active galactic nuclei (AGN). In this paradigm absorption is only witnessed in (close to) type-2 objects, where the central obscuration is viewed (nearly) edge-on and thus absorbs the rest frame 1420 MHz emission along our sight-line. However, we find this mix of detections and non-detections to only apply at low redshift (z < 1): From a sensitive survey of eight z > 3 radio sources we find no 21-cm absorption, indicating a low abundance of cold neutral gas in (the sight-lines searched in) these objects. Analysing the spectral energy distributions of these sources, we find that our high redshift selection introduces a bias where our sample consists exclusively of quasars with ultra-violet luminosities in excess of 10e23 W/Hz. This may suggest that we have selected a class of particularly UV bright type-1 objects. Whatever the cause, it must also be invoked to explain the non-detections in an equal number of z < 0.7 sources, where we find, for the first time, the same exclusive non-detections at > 10e23 W/Hz. These objects also turn out to be quasars and, from these exclusive high UV luminosity--21-cm non-detections, it is apparent that orientation effects alone cannot account for the mix of 21-cm detections and non-detections at any redshift.
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