The first spectroscopic dust reverberation programme on active galactic nuclei: the torus in NGC 5548
The first spectroscopic dust reverberation programme on active galactic nuclei: the torus in NGC 5548
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DOI：
10.1093/mnras/stz2212
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发表时间：
2019-08
影响因子：
4.8
通讯作者：
H. Landt;M. Ward;D. Kynoch;C. Packham;G. Ferland;A. Lawrence;J. Pott;J. Esser;K. Horne;D. Starkey;D. Malhotra;M. Fausnaugh;B. Peterson;R. Wilman;R. Riffel;T. Storchi-Bergmann;A. Barth;C. Villforth;H. University;University of Texas at San Antonio;Naoj;U. Kentucky;U. Edinburgh;MPIfA;U. S. Andrews;U. I. Urbana-Champaign;Mit;The Ohio State University;Ccapp;Stsci;Universidade Federal de Santa Maria;Universidade Federal do Rio Grande do Sul-Universidade-Federal-do-Rio-Grande-do-Sul-102904658;U. California;Irvine;U. Bath;University of Johannesburg
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作者：
H. Landt;M. Ward;D. Kynoch;C. Packham;G. Ferland;A. Lawrence;J. Pott;J. Esser;K. Horne;D. Starkey;D. Malhotra;M. Fausnaugh;B. Peterson;R. Wilman;R. Riffel;T. Storchi-Bergmann;A. Barth;C. Villforth;H. University;University of Texas at San Antonio;Naoj;U. Kentucky;U. Edinburgh;MPIfA;U. S. Andrews;U. I. Urbana-Champaign;Mit;The Ohio State University;Ccapp;Stsci;Universidade Federal de Santa Maria;Universidade Federal do Rio Grande do Sul-Universidade-Federal-do-Rio-Grande-do-Sul-102904658;U. California;Irvine;U. Bath;University of Johannesburg
我们最近启动了第一个近红外活动星系核尘埃反射光谱方案。光谱法可以测量粉尘特性，如通量、温度和覆盖系数，其精度高于光度法。特别是，它可以测量基于亮度的尘埃半径和尘埃响应时间。在这里，我们报告了NGC 5548上为期1年的活动结果。热尘埃对辐射通量变化的反应滞后时间为1070光日，类似于以前在光度反射活动中发现的情况。的平均值和均方根光谱是相似的，这意味着相同的灰尘成分占主导地位的排放和变化。只有当我们假设一个与波长无关的尘埃发射率定律，即一个黑体时，尘埃滞后时间才与基于亮度的尘埃半径一致，这适用于大尺寸（几μm）的颗粒。对于这样的颗粒，尘埃温度为1450 K。因此，硅酸盐颗粒很可能已经蒸发，碳是主要的化学成分。但与普遍的看法相反，热尘并不接近其升华温度。这进一步得到了我们对与加热/冷却过程基本一致的温度变化的观察的支持。因此，内部的无尘区被扩大，尘埃环面，而不是一个“尘埃墙”，其内径预计是光度不变的。扩大无尘区的沙尘破坏机制似乎也部分影响了有尘区。我们观察到一个周期性减少的尘埃质量与隐含的灰尘改造时间为105 -6个月。
We have recently initiated the first spectroscopic dust reverberation programme on active galactic nuclei in the near-infrared. Spectroscopy enables measurement of dust properties, such as flux, temperature, and covering factor, with higher precision than photometry. In particular, it enables measurement of both luminosity-based dust radii and dust response times. Here we report results from a 1 yr campaign on NGC 5548. The hot dust responds to changes in the irradiating flux with a lag time of ∼70 light-days, similar to what was previously found in photometric reverberation campaigns. The mean and rms spectra are similar, implying that the same dust component dominates both the emission and the variations. The dust lag time is consistent with the luminosity-based dust radius only if we assume a wavelength-independent dust emissivity law, i.e. a blackbody, which is appropriate for grains of large sizes (of a few μm). For such grains the dust temperature is ∼1450 K. Therefore, silicate grains have most likely evaporated and carbon is the main chemical component. But the hot dust is not close to its sublimation temperature, contrary to popular belief. This is further supported by our observation of temperature variations largely consistent with a heating/cooling process. Therefore, the inner dust-free region is enlarged and the dusty torus rather a ‘dusty wall’, whose inner radius is expected to be luminosity-invariant. The dust-destruction mechanism that enlarges the dust-free region seems to also partly affect the dusty region. We observe a cyclical decrease in dust mass with implied dust reformation times of ∼5–6 months.