The Far-Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068
The Far-Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068
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塞弗特星系 NGC 1068 的远红外发射线和连续谱
DOI：
10.1086/428495
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
J. Fischer
中科院分区：
文献类型：
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作者：
L. Spinoglio;M. Malkan;H. Smith;E. González;J. Fischer
利用红外空间天文台（ISO）的长波光谱仪（LWS）观测到了Seyfert 2星系NGC 1068的第一个完整的远红外光谱（43-197 μm）。除了七条预期的离子精细结构发射线外，在79、119和163 μm处的OH旋转线都被检测到发射，这在具有完整LWS光谱的星系中是独一无二的，其中119 μm线在检测时总是处于吸收状态。观测到的线强度与ISO短波光谱仪（SWS）和光学和紫外线强度从文献中一起建模，考虑两个独立的发射分量：活动星系核（AGN）组件和星暴组件的环核约3 kpc的大小。使用紫外到中红外发射线光谱来限制核电离连续谱，我们已经证实了以前的结果：正则幂律电离光谱比深吸收槽的拟合更差，同时排除了“大蓝色凸起”的存在。基于星暴环Brγ等效宽度约束的500万年瞬时星暴年龄，以及中远红外精细结构线辐射的星暴合成模型，导出了低电离参数（U = 10-3.5）和低密度（n = 100 cm-3）。结合活动星系核和星爆的组成部分，我们成功地模拟了NGC 1068的整体UV到远红外原子光谱，重现线通量平均在2.0倍以内，标准差为1.3，整体连续谱是电离和中性成分中热尘埃排放贡献的总和。OH 119 μm的发射表明该谱线是碰撞激发的，产生于温暖致密的区域。OH排放已被建模使用球对称，非本地，非LTE辐射传输模型。模型表明，大部分的排放来自核区域，虽然一些扩展的贡献，从恒星爆发不排除。在核区域中的OH丰度预计为~10-5，这是X射线占主导地位的区域的特征。
We report on the analysis of the first complete far-infrared spectrum (43-197 μm) of the Seyfert 2 galaxy NGC 1068 as observed with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). In addition to the seven expected ionic fine-structure emission lines, the OH rotational lines at 79, 119, and 163 μm were all detected in emission, which is unique among galaxies with full LWS spectra, where the 119 μm line, when detected, is always in absorption. The observed line intensities were modeled together with ISOShort Wavelength Spectrometer (SWS) and optical and ultraviolet line intensities from the literature, considering two independent emission components: the active galactic nucleus (AGN) component and the starburst component in the circumnuclear ring of ~3 kpc in size. Using the UV to mid-IR emission line spectrum to constrain the nuclear ionizing continuum, we have confirmed previous results: a canonical power-law ionizing spectrum is a poorer fit than one with a deep absorption trough, while the presence of a " big blue bump" is ruled out. Based on the instantaneous starburst age of 5 Myr constrained by the Brγ equivalent width in the starburst ring, and starburst synthesis models of the mid- and far-infrared fine-structure line emission, a low-ionization parameter (U = 10-3.5) and low densities (n = 100 cm-3) are derived. Combining the AGN and starburst components, we succeeded in modeling the overall UV to far-IR atomic spectrum of NGC 1068, reproducing the line fluxes to within a factor of 2.0 on average with a standard deviation of 1.3, and the overall continuum as the sum of the contribution of the thermal dust emission in the ionized and neutral components. The OH 119 μm emission indicates that the line is collisionally excited and arises in a warm and dense region. The OH emission has been modeled using spherically symmetric, nonlocal, non-LTE radiative transfer models. The models indicate that the bulk of the emission arises from the nuclear region, although some extended contribution from the starburst is not ruled out. The OH abundance in the nuclear region is expected to be ~10-5, characteristic of X-ray-dominated regions.