Collisional heating as the origin of filament emission in galaxy clusters
Collisional heating as the origin of filament emission in galaxy clusters
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碰撞加热是星系团中灯丝发射的起源
DOI：
10.1111/j.1365-2966.2008.14153.x
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发表时间：
2008
影响因子：
4.8
通讯作者：
R. Williams
中科院分区：
文献类型：
--
作者：
G. Ferland;G. Ferland;A. Fabian;N. Hatch;R. Johnstone;R. Porter;R. Porter;P. V. Hoof;R. Williams
人们早就知道，无论是星光还是其他来源的光致电离，都很难解释观察到的光学细丝的光谱，这些光丝经常环绕在大星团的中心星系周围。这篇文章建立在第一个系列的基础上，在这个系列中，我们研究了高能粒子或耗散磁流体(MHD)波的加热是否可以解释这些观测结果。第一篇论文集中在产生强H2和CO谱线的分子区域。在这里，我们将计算扩展到包括原子和低电离区。对以前的计算进行了两个主要的改进。氢原子的模型，以及类氢等电子序列的所有元素，现在完全是NL分辨的。这使我们能够预测氢发射线光谱，包括超热二次电子和热电子或原子核的激发。我们展示了预测的H-I谱与纯复合情况的不同之处。第二个更新是关于H0-H2非弹性碰撞的速率。我们现在使用Wrathmall等人计算的值。这些速率通常要大得多，并允许无振动的H2能级布居在比之前认为的密度低得多的密度下实现热分布。
我们计算了各种气体密度和碰撞加热速率下的化学、电离、温度、气体压强和发射线光谱。我们假定这些细丝受到磁性的限制。气体可以沿着场线自由移动，因此气体压力等于周围热气体的压力。可能存在一种混合的云，一些是稠密而寒冷的，另一些是热的和稀薄的。观测到的光谱将是不同密度和温度但气压相同的云的综合发射P/k=nT。我们假设气体填充因子是由密度的幂定律给出的。幂指数是这个理论中唯一的自由参数，它是通过匹配红外H_2线相对于光学H_i线的观测强度来设定的。我们的结论是，这些细丝是由电离粒子加热的，这些粒子要么从周围区域传导进来，要么由与MHD波有关的过程原位产生。
It has long been known that photoionization, whether by starlight or other sources, has difficulty in accounting for the observed spectra of the optical filaments that often surround central galaxies in large clusters. This paper builds on the first of this series in which we examined whether heating by energetic particles or dissipative magnetohydrodynamic (MHD) wave can account for the observations. The first paper focused on the molecular regions which produce strong H2 and CO lines. Here we extend the calculations to include atomic and low-ionization regions. Two major improvements to the previous calculations have been made. The model of the hydrogen atom, along with all elements of the H-like iso-electronic sequence, is now fully nl-resolved. This allows us to predict the hydrogen emission-line spectrum including excitation by suprathermal secondary electrons and thermal electrons or nuclei. We show how the predicted H i spectrum differs from the pure-recombination case. The second update is to the rates for H0–H2 inelastic collisions. We now use the values computed by Wrathmall et al. The rates are often much larger and allow the ro–vibrational H2 level populations to achieve a thermal distribution at substantially lower densities than previously thought.
We calculate the chemistry, ionization, temperature, gas pressure and emission-line spectrum for a wide range of gas densities and collisional heating rates. We assume that the filaments are magnetically confined. The gas is free to move along field lines so that the gas pressure is equal to that of the surrounding hot gas. A mix of clouds, some being dense and cold and others hot and tenuous, can exist. The observed spectrum will be the integrated emission from clouds with different densities and temperatures but the same pressure P/k=nT. We assume that the gas filling factor is given by a power law in density. The power-law index, the only free parameter in this theory, is set by matching the observed intensities of infrared H2 lines relative to optical H i lines. We conclude that the filaments are heated by ionizing particles, either conducted in from surrounding regions or produced in situ by processes related to MHD waves.