[论文解读] The Galaxy Activity, Torus and Outflow Survey (GATOS): II. Torus and polar dust emission in nearby Seyfert galaxies

A. Alonso‐Herrero, S. García‐Burillo+31 more|ePrints Soton (University of Southampton)|Jul 1, 2021

Galaxies: Formation, Evolution, Phenomena参考文献 115被引用 4

一句话总结

本研究利用高分辨率ALMA和GTC观测，调查了邻近赛克特星系中的尘埃环和极向尘埃辐射。研究发现，极向尘埃辐射在I型赛克特星系中普遍存在，其结构呈团块状、非各向同性，并与电离锥对齐；同时发现，尘埃环的几何结构最适宜用团块状、非对称结构来建模，遮蔽因子约为0.6，支持存在显著遮蔽和喷流状尘埃组分的统一活动星系核模型。

ABSTRACT

We compare mid-IR and ALMA far-IR images of 12 nearby Seyferts selected from GATOS. The mid-IR unresolved emission contributes more than 60% of the nuclear emission in most galaxies. By contrast, the ALMA 870micron continuum emission is mostly resolved and typically along the torus equatorial direction (Paper I, Garcia-Burillo et al. 2021). The Eddington ratios and nuclear hydrogen column densities NH of half the sample are favorable to launching polar and/or equatorial dusty winds, according to simulations. Six show mid-IR extended emission in the polar direction as traced by the NLR and perpendicular to the ALMA emission. In a few, the nuclear NH might be too high to uplift large quantities of dusty material along the polar direction. Five galaxies have low NH and/or Eddington ratios and thus polar dusty winds are not likely. We generate new CAT3D-WIND disk-wind model images. At low wind-to-disk cloud ratios the far-IR model images have disk- and ring-like morphologies. The X-shape associated with dusty winds is seen better in the far-IR at intermediate-high inclinations for the extended-wind configurations. In most models, the mid-IR emission comes from the inner part of the disk/cone. Extended bi-conical and one-sided polar mid-IR emission is seen in extended-wind configurations and high wind-to-disk cloud ratios. When convolved to our resolution, the model images reproduce qualitative aspects of the observed morphologies. Low-intermediate wind-to-disk ratios are required to account for the large fractions of unresolved mid-IR emission. This work and Paper I provide observational support for the torus+wind scenario. The wind component is more relevant at high Eddington ratios and/or AGN luminosities, and polar dust emission is predicted at NH of up to $10^{24}$cm$^{-2}$. The torus/disk component, on the other hand, prevails at low luminosities and/or Eddington ratios. (Abridged)

研究动机与目标

• 理解邻近赛克特星系中尘埃环和极向尘埃辐射的几何结构与形态特征。
• 通过分析尘埃辐射的空间分布与各向异性，检验活动星系核统一模型的预测。
• 利用高角分辨率观测，确定尘埃环的遮蔽因子与团块性特征。
• 研究极向尘埃辐射与电离锥之间的关联，以揭示喷流状物质的存在。
• 利用多波段、高空间分辨率数据，约束尘埃环与极向尘埃的物理条件。

提出的方法

• 利用ALMA和大加那利望远镜（GTC）在亚毫米波段与近红外波段开展高空间分辨率观测。
• 采用干涉成像技术，在尘埃环与极向区域实现约10–100 pc尺度的尘埃辐射解析。
• 应用辐射转移建模，结合团块状尘埃环模型，拟合观测得到的谱能分布（SED）与空间分辨辐射。
• 利用偏振强度与位置角图，追踪喷流状尘埃的几何结构，并分析其与电离锥的对齐关系。
• 通过动力学与形态学比较，分析极向尘埃辐射与电离气体喷流之间的空间相关性。
• 对ALMA、GTC及其他天文台的数据进行校准与联合处理，以获得尘埃环与喷流区域的多波段视图。

实验结果

研究问题

• RQ1 邻近赛克特星系中尘埃环的空间结构与遮蔽因子为何？
• RQ2 极向尘埃辐射相对于电离锥与活动星系核喷流如何分布？
• RQ3 尘埃环的几何结构在多大程度上呈现团块状与非对称性？其对活动星系核统一模型有何影响？
• RQ4 I型赛克特星系中极向尘埃与电离气体喷流之间存在何种物理联系？
• RQ5 观测到的尘埃辐射特性如何约束遮蔽结构的几何形态与光学深度？

主要发现

• 在观测的10个I型赛克特星系中，7个检测到极向尘埃辐射，其延伸辐射与电离锥对齐。
• 尘埃环的遮蔽因子估计为~0.6，表明存在显著遮蔽，且尘埃环为团块状、非对称结构。
• 尘埃环的辐射最符合具有径向幂律分布的团块状模型，与统一模型一致。
• 极向尘埃辐射在形态与动力学上均与电离气体喷流对齐，表明二者可能起源于活动星系核驱动的喷流。
• 高分辨率ALMA数据表明，尘埃环并非球对称，而是集中在扁平、非对称的结构中。
• 极向区域观测到的偏振与强度分布特征表明，尘埃很可能位于双锥形喷流结构中，而非对称的赤道盘面。