Charge-exchange X-ray emission of nearby star-forming galaxies
Charge-exchange X-ray emission of nearby star-forming galaxies
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DOI：
10.1111/j.1365-2966.2011.20263.x
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发表时间：
2011-11
影响因子：
4.8
通讯作者：
Jiren Liu;Q. Wang;S. Mao
中科院分区：
文献类型：
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作者：
Jiren Liu;Q. Wang;S. Mao
星系热气体外流的性质通常是由伴随X射线辐射来测量的，它代表热激发热气体中的原子跃迁。然而，X射线谱线发射也可以由高度电离的离子和中性物质之间的电荷交换引起。类He离子的Kα三重态可以作为一种强有力的诊断方法，因为电荷交换X射线发射（CXE）有利于相互结合线和禁戒线，而热发射有利于共振线。我们分析了由XMM-牛顿反射光栅光谱仪观测到的9个附近恒星形成星系的样本的O VII三重态。对于大多数星系，禁戒内斯与共振线相当或更强，这与热预测相反。对于NGC 253、M51、M83、M61、NGC 4631和银河系，观测到的线比与CXE的线比一致;对于M94和NGC 2903，观测到的线比表明有多个起源;对于M82，不同区域的线比不同，也表明有多个起源。我们讨论了其他可能的机制，可以产生一个相对较强的禁戒线，如碰撞非平衡电离复合/电离等离子体，这是不利的。这些结果表明，CXE可能是一个共同的过程，并作出贡献的大质量星星形成的星系的软X射线线发射的显着部分。
Properties of hot gas outflows from galaxies are generally me asured from associated Xray line emission assuming that it represents atomic transi tions in thermally excited hot gas. X-ray line emission, however, can also arise from the charge exchange between highly ionised ions and neutral species. The Kα triplet of He-like ions can be used as a powerful diagnostic, because the charge exchange X-ray emission (CXE) favours the inter-combination and forbidden lines, while the thermal emission favours the resonance line. We analyse the O VII triplet of a sample of nine nearby star-forming galaxies observed by the XMM-Newton reflection grating spectrometers. For most galaxies, the forbidden li nes are comparable to or stronger than the resonance lines, which is in contrast to the thermal prediction. For NGC 253, M51, M83, M61, NGC 4631, and the Antennae galaxy, the observed line ratios are consistent with the ratio of the CXE; for M94 and NGC 2903, the observed ratios indicate multiple origins; for M82, different regions show different line ratios, also indicating multiple origins. We dis cuss other possible mechanisms that can produce a relatively strong forbidden line, such as a collisional non-equilibrium-ionization recombining/ionizing plasma, which are not favoured. These results suggest that the CXE may be a common process and contribute a significant fraction of the soft X-ray line emission for galaxies with massive star formation.