The Near-infrared CO Absorption Band as a Probe to the Innermost Part of an AGN-obscuring Material
The Near-infrared CO Absorption Band as a Probe to the Innermost Part of an AGN-obscuring Material
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DOI：
10.3847/1538-4357/aa9f25
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发表时间：
2017-12
期刊：
影响因子：
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通讯作者：
S. Baba;T. Nakagawa;N. Isobe;M. Shirahata
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文献类型：
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作者：
S. Baba;T. Nakagawa;N. Isobe;M. Shirahata
我们系统地分析了4.67μm CO向附近活动星系核(AGN)的旋转振动吸收带，并分析了从Akari和Spitzer光谱观测中收集到的10个附近星系的吸收轮廓，通过一个平面平行的局域热平衡气体模型拟合了CO的吸收特征。我们发现，CO气体是温暖的(200-500K)，并且具有较大的柱密度()。气体的加热既不能用紫外线加热，也不能用冲击加热来解释，因为这些过程不能代表温暖气体的大柱密度。相反，来自原子核的X射线光子是最令人信服的能量来源，它可以产生高达30%的大柱热气体。从CO带估计的氢柱密度比从X射线观测推断的要小。这些结果表明，近红外CO吸收探测到的区域位于原子核附近，位于X射线发射区之外。此外，观测到的深吸收剖面所要求的接近一致的覆盖因子表明，探测区域靠近连续谱源，这可以被指定为活动星系核周围遮挡物质的内缘。
We performed a systematic analysis of the 4.67 μm CO ro-vibrational absorption band toward nearby active galactic nuclei (AGNs) and analyzed the absorption profiles of 10 nearby galaxies collected from the AKARI and Spitzer spectroscopic observations that show the CO absorption feature by fitting a plane-parallel local thermal equilibrium gas model. We found that CO gas is warm (200–500 K) and has a large column density ( ). The heating of the gas is not explicable by either UV heating or shock heating because these processes cannot represent the large column densities of the warm gas. Instead, X-ray photons from the nuclei, which can produce large columns of warm gas with up to , are the most convincing power source. The hydrogen column density estimated from the CO band is smaller than that inferred from X-ray observations. These results indicate that the region probed by the near-infrared CO absorption is in the vicinity of the nuclei and is located outside the X-ray emitting region. Furthermore, the covering factors of nearly unity required by the observed deep absorption profiles suggest that the probed region is close to the continuum source, which can be designated as the inner rim of the obscuring material around the AGN.