[论文解读] New AGN diagnostic diagrams based on the [OIII]$λ4363$ auroral line

Giovanni Mazzolari, Hannah Übler+9 more|arXiv (Cornell University)|Apr 16, 2024

Cardiovascular Syncope and Autonomic Disorders被引用 6

一句话总结

本文介绍了三种基于休止帧光学诊断图，用 [OIII]λ4363 远日线来识别AGN，利用 JWST 可获得的谱线，并通过大量局部和高红移样本以及光电离模型进行测试。

ABSTRACT

The James Webb Space Telescope (JWST) is revolutionizing our understanding of black holes formation and growth in the early Universe. However, JWST has also revealed that some of the classical diagnostics, such as the BPT diagrams and X-ray emission, often fail to identify narrow line TypeII active galactic nuclei (AGN) at high redshift. Here we present three new rest-frame optical diagnostic diagrams leveraging the [OIII]$\lambda4363$ auroral line, which has been detected in several JWST spectra. Specifically, we show that high values of the [OIII]$\lambda4363/$H$γ$ ratio provide a sufficient (but not necessary) condition to identify the presence of an AGN, both based on empirical calibrations (using local and high-redshift sources) and a broad range of photoionization models. These diagnostics are able to separate much of the AGN population from Star Forming Galaxies (SFGs). This is because the average energy of AGN's ionizing photons is higher than that of young stars in SFGs, hence AGN can more efficiently heat the gas, therefore boosting the [OIII]$\lambda4363$ line. We also found independent indications of AGN activity in some high-redshift sources that were not previously identified as AGN with the traditional diagnostics diagrams, but that are placed in the AGN region of the diagnostics presented in this work. We note that, conversely, low values of [OIII]$\lambda4363/$H$γ$ can be associated either with SFGs or AGN excitation. We note that the fact that strong auroral lines are often associated with AGN does not imply that they cannot be used for direct metallicity measurements (provided that proper ionization corrections are applied), but it does affect the calibration of strong line metallicity diagnostics.

研究动机与目标

• 激励在高红移下需要新的 AGN 诊断方法，因为传统图在 JWST 数据下失效。
• 提出三种基于 [OIII]4363 及互补线的休止帧光学诊断，以将 AGN 与 SFGs（星形成星系）区分开。
• 针对局部和高-z样本及光电离模型对诊断进行校准与验证。
• 讨论在金属丰度估计和离子化条件方面，AGN 与星形成星系之间的差异对诊断的含义。

提出的方法

• 汇编大量局部和高-z 的观测样本，检测到 [OIII]λ4363 通量（SFGs 与 AGN）。
• 构建三种新的诊断图，将 [OIII]λ4363/Hγ 与 (a) [OIII]5007/[OII]3727、(b) [NeIII]3869/[OII]3727、(c) [OIII]5007/[OIII]4363 比例结合起来。
• 将观测分布与光电离模型网格（Gutkin+2016、Feltre+2016）以及 Nakajima & Maiolino (2022) 的变体进行比较。
• 在金属丰度–电离参数空间内应用基于似然的裁剪，以剔除不物理的 SFG 模型。
• 评估红化效应以及跨红移的 AGN 区分鲁棒性。

Figure 1 : Diagnostic diagram showing the [OIII] $\lambda 4363\,$ /H $\gamma\ $ vs [OIII] $\lambda 5007\,$ /[OII] $\lambda 3727\,$ lines ratios. The [OII] $\lambda 3727\,$ is the sum of the doublet [OII] $\lambda\lambda 3726,3728$ . Left panel: plot of all the observational samples described in Sec.

实验结果

研究问题

• RQ1 将 [OIII]λ4363/Hγ 与其他近红外线比结合，是否能在低红移和高红移下可靠地区分 AGN 与星形成星系？
• RQ2 光电离模型是否能再现新图中充满 AGN 的区域，并在整个参数空间中将它们与 SFGs 区分开？
• RQ3 尘埃红化对星系在这些图中的定位有何影响，诊断在高 z 下是否仍然稳健？
• RQ4 这些诊断对使用 [OIII]4363 及相关强线标定的金属丰度测量有何影响？
• RQ5 是否有通过 JWST 在高-z 观察到的星系，在传统图中并未被判定为 AGN，但在这些新图中位于 AGN 区域？

主要发现

• 三种基于 [OIII]λ4363/Hγ，并结合 [OIII]5007/[OII]3727、[NeIII]3869/[OII]3727，或 [OIII]5007/[OIII]4363 的新诊断，在局部与高-z 样本中有效地区分 AGN 与 SFGs。
• AGN 群体位于纯 SFG 模型无法达到的区域，而大量 SFGs 在所有图中仍然不被归入 AGN 区域。
• 一些此前未被识别为 AGN 的高-z 来源落在这些图的 AGN 区域，表明 JWST 数据中的 AGN 指示信号增强。
• 由于离子化光谱更硬，AGNs 的[OIII]4363 远日线发射增强，使得在合适的离子化修正下可进行基于温度的金属丰度考虑。
• 尘埃红化会使对象在图中移动，可能会改变以 AGN 为主的源的位置，但在典型红化下，SFGs 不太可能污染 AGN 区域。
• 模型比较显示 SFG 网格很少达到 AGN 区域，而 AGN 网格覆盖两者区域，包括观测到的 AGN 所出现的区域。
• 该工作强调重新评估依赖 [OIII]4363 的金属丰度标定，特别是在 AGN 影响下的意义。

Figure 2 : Same as in Fig. 1 , but for the lines ratios [OIII] $\lambda 4363\,$ /H $\gamma\ $ vs [Ne III] $\lambda 3869\ $ /[OII] $\lambda 3727\,$ . Based on the distribution of observational samples and models, also this diagnostic diagram identifies a region that can be populated only by AGN.