Excitation mechanisms in the intracluster filaments surrounding brightest cluster galaxies
Excitation mechanisms in the intracluster filaments surrounding brightest cluster galaxies
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最亮星团星系周围星团内细丝的激发机制
DOI：
10.1051/0004-6361/202039730
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发表时间：
2021
影响因子：
6.5
通讯作者：
Dubois, Y.
中科院分区：
文献类型：
--
作者：
Polles, F. L.;Salomé, P.;Guillard, P.;Godard, B.;Pineau des Forêts, G.;Olivares, V.;Beckmann, R. S.;Canning, R. E.;Combes, F.;Dubois, Y.
冷核星系团中心的巨型椭圆星系(又称最亮星系团)周围丝状气体结构的激发，对于我们理解活动星系核(AGN)的反馈，以及环境和局域效应对恒星形成的影响是关键。目的研究活动星系核周围冷却流动的热辐射对星团激发的贡献。我们探讨了小水平的额外加热(湍流)和金属丰度对光学和红外线的影响。方法使用云程序，我们模拟了光学厚度为30mag的一块气体在恒压下的光致电离和光解，以便自洽地计算从电离气体到分子气体的所有气相。电离源是冷却气体发出的极紫外线(EUV)和软X射线辐射。我们测试了这些模型，将它们的预测与现在在冷核星系团中实现的从光学到亚毫米的丰富的多波长观测进行了比较。结果这样的自辐射云模型，当达到足够大的AV时，会导致云结构的电离、原子和分子气相。这些模型再现了在BCG周围的星云中观察到的大多数多波长光谱，不仅如光学诊断、[O III]λ5007？/Hβ、[N II]λ6583？/Hα和([S II]λ6716？+[S II]λ6731？)/Hα等低电离核发射区，而且还包括原子气体的红外发射线。相反，除了非常低的AV外，在整个参数空间中高估了[O I]λ6300？/Hα。模拟的环振动H_2线也与观测结果相吻合，这表明近红外和中红外H_2线主要是由于H_2分子与云内自然产生的二次电子之间的碰撞而激发的，这些二次电子是由X射线和灯丝中的冷气体相互作用而产生的。然而，电离线示踪剂和分子线示踪剂(即CO)之间仍然存在一定的张力，这需要优化云层结构和分子带密度。尽管参数空间存在简并现象，但预测与观测匹配的有限参数范围允许我们约束沐浴细丝的X射线辐射强度，以及它们的一些物理性质，如AV值或湍流加热率水平。结论等离子体冷却产生的EUV和X射线辐射的再处理是BCG周围细丝线发射的重要动力源。当所有气相(从电离到分子)被自洽地模拟时，结合少量湍流加热的云状自辐射X射线激发模型设法同时再现大量的光学与红外线比率。释放我们模型的一些简化，如恒定压力，或者添加来自活动星系核和恒星的辐射场，以及物质和辐射受限的云分布的组合，应该会改善对不同气相的线发射的预测。
ContextThe excitation of the filamentary gas structures surrounding giant elliptical galaxies at the center of cool-core clusters, also known as brightest cluster galaxies (BCGs), is key to our understanding of active galactic nucleus (AGN) feedback, and of the impact of environmental and local effects on star formation.AimsWe investigate the contribution of thermal radiation from the cooling flow surrounding BCGs to the excitation of the filaments. We explore the effects of small levels of extra heating (turbulence), and of metallicity, on the optical and infrared lines.MethodsUsing the CLOUDY code, we modeled the photoionization and photodissociation of a slab of gas of optical depthAV≤ 30 mag at constant pressure in order to calculate self-consistently all of the gas phases, from ionized gas to molecular gas. The ionizing source is the extreme ultraviolet (EUV) and soft X-ray radiation emitted by the cooling gas. We tested these models comparing their predictions to the rich multi-wavelength observations from optical to submillimeter, now achieved in cool core clusters.ResultsSuch models of self-irradiated clouds, when reaching sufficiently largeAV, lead to a cloud structure with ionized, atomic, and molecular gas phases. These models reproduce most of the multi-wavelength spectra observed in the nebulae surrounding the BCGs, not only the low-ionization nuclear emission region like optical diagnostics, [O III]λ5007 Å/Hβ, [N II]λ6583 Å/Hα, and ([S II]λ6716 Å+[S II]λ6731 Å)/Hα, but also the infrared emission lines from the atomic gas. [O I]λ6300 Å/Hα, instead, is overestimated across the full parameter space, except for very lowAV. The modeled ro-vibrational H2lines also match observations, which indicates that near- and mid-infrared H2lines are mostly excited by collisions between H2molecules and secondary electrons produced naturally inside the cloud by the interaction between the X-rays and the cold gas in the filament. However, there is still some tension between ionized and molecular line tracers (i.e., CO), which requires optimization of the cloud structure and the density of the molecular zone. The limited range of parameters over which predictions match observations allows us to constrain, in spite of degeneracies in the parameter space, the intensity of X-ray radiation bathing filaments, as well as some of their physical properties likeAVor the level of turbulent heating rate.ConclusionsThe reprocessing of the EUV and X-ray radiation from the plasma cooling is an important powering source of line emission from filaments surrounding BCGs. CLOUDY self-irradiated X-ray excitation models coupled with a small level of turbulent heating manage to simultaneously reproduce a large number of optical-to-infrared line ratios when all the gas phases (from ionized to molecular) are modeled self-consistently. Releasing some of the simplifications of our model, like the constant pressure, or adding the radiation fields from the AGN and stars, as well as a combination of matter- and radiation-bounded cloud distribution, should improve the predictions of line emission from the different gas phases.
Abell 478 中冷却流的光谱特征
DOI：
--
发表时间：
1992
期刊：
影响因子：
--
作者：
R. Johnstone;A. Fabian;A. Edge;P. Thomas
通讯作者：
P. Thomas