The Ionization Structure of the Narrow-Line Region of NGC 1068 and Its Relationship to the Extended Radio Emission
The Ionization Structure of the Narrow-Line Region of NGC 1068 and Its Relationship to the Extended Radio Emission
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NGC 1068窄线区电离结构及其与扩展射电发射的关系
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发表时间：
1997
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影响因子：
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通讯作者：
F. Macchetto
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作者：
A. Capetti;D. Axon;F. Macchetto
利用哈勃太空望远镜(HST)/WFPC2成像技术研究了Seyfert 2星系NGC1068窄线区的发射线结构及其与扩展射电辐射的关系。我们发现NGC1068的NLR的形态和电离性质是由与射电喷流的相互作用决定的，这与对其他具有扩展射电发射的塞弗特星系的类似结果完全一致。发射线起源于两个不同的区域：覆盖着东北部射电波瓣的大规模蚕茧和围绕射电喷流的由细丝和结组成的小规模破碎网络。沿着射电喷流的物质，虽然密度比周围的气体高，但比NLR的其余部分处于更高的电离态。我们认为，这需要存在一个在当地支配核发射的电离辐射源，例如，通过与射电喷流相互作用而加热的气体的自由发射。在距原子核约4‘(~300pC)的距离处，对应于射电结构从喷口状到半球状的转变，NLR的电离结构在内部低电离区和外部高电离区之间显示出清晰而明确的边界。这种电离变化很容易解释，如果在喷流进入波瓣的地方有密度增加，推测是由于喷流工作面上倒流的无线电茧的压缩。彩色图像显示了投射到隐藏的原子核位置上的核尘埃通道的存在。在用HST观测到的Seyfert 2星系中，核尘埃带似乎无处不在，并且可以自然地与导致活动核遮挡的物质有关。
Hubble Space Telescope (HST)/WFPC2 imaging has been used to investigate the emission-line structure of the narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 and its relationship to the extended radio emission. We find that the morphology and the ionization properties of the NLR of NGC 1068 are dominated by the interaction with the radio jet, in full agreement with similar results obtained for other Seyfert galaxies with extended radio emission. The emission lines originate in two distinct regions: a large-scale cocoon enveloping the northeastern radio lobe and a small-scale broken network of filaments and knots surrounding the radio jet. The material along the radio jet, although denser than the surrounding gas, is in a much higher ionization state than the remainder of the NLR. We believe that this requires the presence of a source of ionizing radiation that locally dominates over the nuclear emission, e.g., free-free emission from the gas heated by the interaction with the radio jet. At a distance of approximately 4' (~300 pc) from the nucleus, corresponding to the transition in the radio structure from jetlike to lobelike, the ionization structure of the NLR shows a sharp and well-defined boundary between an inner low-ionization zone and an outer higher ionization zone. This ionization change is easily explained if there is a density increase where the jet enters the lobe, presumably due to the compression of the backflowing radio cocoon at the jet working surface. A color image reveals the presence of a nuclear dust lane projected onto the location of the hidden nucleus. Nuclear dust lanes appear to be ubiquitous in Seyfert 2 galaxies observed with HST and can be naturally associated with the material responsible for the obscuration of the active nucleus.