用中红外和近红外干涉仪探测AGN的最内层尘埃结构
Probing the innermost dusty structure in AGN with mid-IR and near-IR interferometers
摘要：
利用中红外和近红外长基线干涉仪，我们现在正在亚PC尺度上绘制活动星系核中尘埃吸积物质的径向分布。我们目前专注于1型活动星系核，其中最内层的区域是清晰的，其内在结构可以直接研究。作为第一个系统的研究类型1的，我们获得了中/近红外数据的小样本超过约3-4个数量级的UV光度L的中央引擎。在这里，我们通过观察被中央引擎辐射加热的尘埃颗粒来有效地追踪结构。与对这种尘埃颗粒的天真期望一致，尘埃升华半径R_in实际上是根据近红外混响测量的经验已知的与L^1/2成比例，这也得到了我们的近红外干涉测量的支持。利用这一经验关系，我们通过R_in对径向范围进行归一化，并消除简单的L^1/2标度，以便在样本上进行直接比较。然后我们发现，在中红外，在更高的光度源中，以R_in为单位的整体尺寸似乎变得更紧凑。更具体地说，中红外亮度分布是相当好地描述了一个幂律，这个幂律变得更陡峭，在更高的光度对象。近红外通量似乎不是中红外幂律分量向短波长的简单向内外推，而是来自尘埃分布的内缘区域的一个小的明显亮度集中。它的结构还没有得到很好的限制，但有初步证据表明，这种内部近红外发射结构在喷气发射物体中具有更陡峭的径向分布。所有这些都应该通过进一步的观察来仔细研究。
英文摘要：
With mid-IR and near-IR long-baseline interferometers, we are now mapping the radial distribution of the dusty accreting material in AGNs at sub-pc scales. We currently focus on Type 1 AGNs, where the innermost region is unobscured and its intrinsic structure can be studied directly. As a first systematic study of Type 1s, we obtained mid-/near-IR data for small samples over ~3-4 orders of magnitudes in UV luminosity L of the central engine. Here we effectively trace the structure by observing dust grains that are radiatively heated by the central engine. Consistent with a naive expectation for such dust grains, the dust sublimation radius R_in is in fact empirically known to be scaling with L^1/2 from the near-IR reverberation measurements, and this is also supported by our near-IR interferometry. Utilizing this empirical relationship, we normalize the radial extent by R_in and eliminate the simple L^1/2 scaling for a direct comparison over the samples. We then find that, in the mid-IR, the overall size in units of R_in seems to become more compact in higher luminosity sources. More specifically, the mid-IR brightness distribution is rather well described by a power-law, and this power-law becomes steeper in higher luminosity objects. The near-IR flux does not seem to be a simple inward extrapolation of the mid-IR power-law component toward shorter wavelengths, but it rather comes from a little distinct brightness concentration at the inner rim region of the dust distribution. Its structure is not well constrained yet, but there is tentative evidence that this inner near-IR-emitting structure has a steeper radial distribution in jet-launching objects. All these should be scrutinized with further observations.
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