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arXiv 2302.12437astro-ph.GA
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利用光学与中红外集合结构函数约束AGN环面尺寸

Constraining AGN Torus Sizes with Optical and Mid-Infrared Ensemble Structure Functions

Junyao Li, Yue Shen

AI总结:

提出利用光学与中红外集合结构函数约束AGN尘埃环面尺寸的新方法,通过模拟和587个SDSS类星体验证其有效性,测得R-L关系且对数据质量要求更低。

摘要:

我们提出了一种新方法,利用光学和中红外(MIR)集合结构函数(SFs)来约束宽线区活动星系核(AGNs)中尘埃环面的尺寸。由于环面的几何稀释效应,MIR对光学连续谱变化的响应表现出相对于光学的受抑变化性,这取决于环面的几何结构(如尺寸、方向、开口角)。更延展的环面相对于光学SFs具有更陡峭的MIR SFs。我们使用模拟的AGN光变曲线和几何环面模型证明了这种SF方法的可行性。由于SF对这些参数不敏感,很难用SFs约束方向和开口角,但环面的尺寸可以被很好地确定。将该方法应用于587个SDSS类星体的集合SFs,我们在WISE W1波段测得环面的R-L关系为log R_eff (pc) = 0.51_{-0.04}^{+0.04} × log (L_bol/10^46 erg s^-1) - 0.38_{-0.01}^{+0.01},在W2波段的尺寸约大1.4倍,这与尘埃反响映射测量结果高度一致。与反响映射技术相比,SF方法对数据质量的要求低得多,只要变化过程和环面结构是稳态的,即可应用于任何无法进行延迟测量的光学+MIR光变曲线。虽然该SF方法不能提取光变曲线中的所有信息(即传递函数),但它为观测到的AGN MIR SFs相对于光学SFs的趋势提供了直观解释。

英文摘要:

We propose a new method to constrain the size of the dusty torus in broad-line active galactic nuclei (AGNs) using optical and mid-infrared (MIR) ensemble structure functions (SFs). Because of the geometric dilution of the torus, the MIR response to optical continuum variations has suppressed variability with respect to the optical that depends on the geometry (e.g., size, orientation, opening angle) of the torus. More extended tori have steeper MIR SFs with respect to the optical SFs. We demonstrate the feasibility of this SF approach using simulated AGN light curves and a geometric torus model. While it is difficult to use SFs to constrain the orientation and opening angle due to insensitivity of the SF on these parameters, the size of the torus can be well determined. Applying this method to the ensemble SFs measured for 587 SDSS quasars, we measure a torus $R-L$ relation of ${\rm log}\,R_{\rm eff}\, {(\rm pc)} = 0.51_{-0.04}^{+0.04} \times {\rm log}\,(L_{\rm bol}/10^{46}\,\rm erg\,s^{-1}) -0.38_{-0.01}^{+0.01}$ in the WISE $W1$ band, and sizes $\sim1.4$ times larger in the $W2$ band, which are in good agreement with dust reverberation mapping measurements. Compared with the reverberation mapping technique, the SF method is much less demanding in data quality and can be applied to any optical+MIR light curves for which a lag measurement may not be possible, as long as the variability process and torus structure are stationary. While this SF method does not extract all information contained in the light curves (i.e., the transfer function), it provides an intuitive interpretation for the observed trends of AGN MIR SFs compared with optical SFs.

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