解开半人马座A的环核环境：II。论宽吸收线的本质
Disentangling the circumnuclear environs of Centaurus A: II. On the nature of the broad absorption line
摘要：
本文报道了最近的强射电星系半人马座A（NGC 5128）的原子气体（HI）和分子气体（CO（2-1）示踪）的红移吸收特征。我们的HI观测使用甚长基线阵列，使我们能够辨别前所未有的sub-parsec分辨率HI吸收剖面朝向不同的位置沿21厘米连续喷流发射内0。“3（或5.4个百分点）。此外，我们的CO（2-1）数据获得的亚毫米阵列探测的吸收分子气体的大部分几乎没有污染的排放，不可能与以前的CO单碟观测。我们用这些数据阐明了视线中气体的物理性质，强调了关于产生宽吸收线（~55 km/s）的气体性质的仍然公开的争论。首先，宽的H I谱线在中心最亮的21 cm连续谱分量上比在喷流附近20 mas（或0.4 pc）处更突出，这表明宽的吸收谱线来自于靠近核的气体，而不是来自于扩散的更远的气体。第二，在CO（2-1）吸收光谱中检测到的不同速度分量与其他分子谱线（例如HCO+（1-0）的谱线）匹配良好，除了在HCO+（1-0）中检测到的宽吸收谱线（并且最可能与H I的谱线相关）。活动星系核引起的分子氢的解离在<= 10 pc的距离上似乎是有效的，这可能有助于宽的H I和分子线的深度。
英文摘要：
We report on atomic gas (HI) and molecular gas (as traced by CO(2-1)) redshifted absorption features toward the nuclear regions of the closest powerful radio galaxy, Centaurus A (NGC 5128). Our HI observations using the Very Long Baseline Array allow us to discern with unprecedented sub-parsec resolution HI absorption profiles toward different positions along the 21 cm continuum jet emission in the inner 0."3 (or 5.4 pc). In addition, our CO(2-1) data obtained with the Submillimeter Array probe the bulk of the absorbing molecular gas with little contamination by emission, not possible with previous CO single-dish observations. We shed light with these data on the physical properties of the gas in the line of sight, emphasizing the still open debate about the nature of the gas that produces the broad absorption line (~55 km/s). First, the broad H I line is more prominent toward the central and brightest 21 cm continuum component than toward a region along the jet at a distance ~ 20 mas (or 0.4 pc) further from it. This suggests that the broad absorption line arises from gas located close to the nucleus, rather than from diffuse and more distant gas. Second, the different velocity components detected in the CO(2-1) absorption spectrum match well other molecular lines, such as those of HCO+(1-0), except the broad absorption line that is detected in HCO+(1-0) (and most likely related to that of the H I). Dissociation of molecular hydrogen due to the AGN seems to be efficient at distances <= 10 pc, which might contribute to the depth of the broad H I and molecular lines.
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