AGN环面的最里面区域：来自HST/NICMOS 1型点源和近红外混响的暗示
The innermost region of AGN tori: implications from the HST/NICMOS Type 1 point sources and near-IR reverberation
摘要：
活动星系核最内层环面的空间分辨是其高空间分辨率研究的主要目标之一。这可以在1型活动星系核的近红外观测中完成，在那里我们直接看到环面中最热的尘埃颗粒。我们讨论两个关键问题，在这样的研究。首先，我们研究了邻近第一型活动星系核的HST/NICMOS图像中的核点源，以评估来自中央假定的吸积盘的可能贡献。经过仔细减去主机隆起通量，我们表明，近红外颜色的点源出现相当简单的解释作为一个复合物的黑体光谱和一个相对蓝色的独特的组件预期的环面和吸积盘，分别。我们的辐射转移模型clustraltori也支持这个简单的两个组件的解释。所观察到的近红外颜色表明，在2.2微米处的分数吸积盘贡献为~25%或更少。其次，我们表明，最近的近红外混响测量所示的最内层环面半径系统小于约3倍，比预测的尘埃升华半径与升华温度为1500 K和尺寸为0.05微米的半径石墨颗粒的合理假设。这种差异可能表明在最里面的环面中升华温度要高得多，或者典型的晶粒尺寸要大得多，尽管前一种情况似乎不受上面研究的HST点源的观测颜色的影响。基线约为100米的近红外干涉测量法应能根据上面获得的低吸积盘贡献提供重要的独立尺寸测量。
英文摘要：
Spatially resolving the innermost torus in AGN is one of the main goals of its high-spatial-resolution studies. This could be done in the near-IR observations of Type 1 AGNs where we see directly the hottest dust grains in the torus. We discuss two critical issues in such studies. Firstly, we examine the nuclear point sources in the HST/NICMOS images of nearby Type 1 AGNs, to evaluate the possible contribution from the central putative accretion disk. After a careful subtraction of host bulge flux, we show that near-IR colors of the point sources appear quite interpretable simply as a composite of a black-body-like spectrum and a relatively blue distinct component as expected for a torus and an accretion disk, respectively. Our radiative transfer models for clumpy tori also support this simple two-component interpretation. The observed near-IR colors suggest a fractional accretion disk contribution of ~25% or less at 2.2 micron. Secondly, we show that the innermost torus radii as indicated by the recent near-IR reverberation measurements are systematically smaller by a factor of ~3 than the predicted dust sublimation radius with a reasonable assumption for graphite grains of sublimation temperature 1500 K and size 0.05 micron in radius. The discrepancy might indicate a much higher sublimation temperature or a typical grain size being much larger in the innermost tori, though the former case appears to be disfavored by the observed colors of the HST point sources studied above. The near-IR interferometry with a baseline of ~100 m should be able to provide the important, independent size measurements, based on the low accretion disk contribution obtained above.
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