We investigate spatial distributions of iron Kα (Fe-Kα) lines in the cental 100 pc of the Seyfert 2 galaxy NGC 1068 observed with Chandra. The spatial distributions of Fe-Kα lines, neutral and highly ionized, around the center of the galactic nucleus are not isotropic, as consistently confirmed in both image and spectral analyses. The hydrogen number density of the gas clouds responsible for the neutral Fe-Kα line emission is estimated to be 102–103 cm−3 for the sampled regions near the galactic core. The photo-ionization model, where iron is assumed to be ionized by X-rays from the galactic nucleus, yields ionization parameters lower than 19 for these clouds. The range of this ionization parameter is two or three orders of magnitude lower than the theoretically expected value to produce the observed helium-like Fe-Kα line intensities. Therefore, the photo-ionization model is excluded from the explanation of the amount of highly ionized iron that is responsible for the observed Fe-Kα lines. Also, we find anti-correlation in the spatial distributions between the molecular cloud in the area observed with ALMA and that of the Fe-Kα lines, including that from neutral iron. We suggest that X-ray iron-line and radio molecular cloud observations are complementary to probe the distribution of matters in the central regions around the cores of active galactic nuclei.

中文翻译：

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原型 2 型活动星系核 NGC 1068 与钱德拉的空间分辨 X 射线光谱

我们研究了用钱德拉观测到的 Seyfert 2 星系 NGC 1068 的中心 100 pc 中铁 Kα (Fe-Kα) 线的空间分布。正如图像和光谱分析一致证实的那样，围绕银河核中心的中性和高度电离的 Fe-Kα 线的空间分布不是各向同性的。对于靠近银河系核心的采样区域，负责中性 Fe-Kα 线发射的气体云的氢数密度估计为 102-103 cm-3。假设铁被来自银河核的 X 射线电离的光电离模型，产生的这些云的电离参数低于 19。该电离参数的范围比理论预期值低两个或三个数量级，以产生观察到的类氦 Fe-Kα 线强度。所以，光电离模型被排除在对导致观察到的 Fe-Kα 线的高度电离铁量的解释之外。此外，我们发现用 ALMA 观察到的区域中的分子云与 Fe-Kα 线（包括中性铁的分子云）之间的空间分布存在反相关性。我们建议 X 射线铁线和射电分子云观测相辅相成，以探测活动星系核核心周围中心区域的物质分布。