SPECTRAL MODELING OF THE CHARGE-EXCHANGE X-RAY EMISSION FROM M82
SPECTRAL MODELING OF THE CHARGE-EXCHANGE X-RAY EMISSION FROM M82
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DOI：
10.1088/0004-637x/794/1/61
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发表时间：
2014-08
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影响因子：
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通讯作者：
Shuinai Zhang;Q. Wang;L. Ji;Randall K. Smith;A. Foster;Xin Zhou
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作者：
Shuinai Zhang;Q. Wang;L. Ji;Randall K. Smith;A. Foster;Xin Zhou
星际气体冷热交界处的电荷交换(CX)过程对恒星形成星系中观测到的软X射线辐射有很大的贡献。我们用新发展的CX模型结合单温热等离子体分析了M82的XMM-牛顿/反射光栅谱仪(RGS)光谱，以表征体积填充的热气体。Cx过程不仅是各类类氦离子Kα三重态的强增强禁带的主要原因，而且也是Cvi(∼87%)、O和Nvii(≳50%)的Lyα跃迁的主要原因。总体而言，在RGS 6-30ä波段中，大约四分之一的X射线通量来自CX。我们推算出S−1在冷热气体界面经历CX的离子入射率为3×1051，∼界面的有效面积为2×1045 cm~2，比全球双子流出的截面大一个数量级。考虑到Cx的贡献，热气体的最佳温度为0.6keV，金属丰度近似为太阳。我们进一步表明，同样的Cx/热等离子体模型也很好地描述了流出帽的EPIC-pn谱，该流出帽距离M82星系盘11.6kpc。这一分析表明，CX可能是恒星暴增星系X射线辐射的重要贡献者，也是探测界面天体物理的宝贵工具。
It has been proposed that the charge-exchange (CX) process at the interface between hot and cool interstellar gases could contribute significantly to the observed soft X-ray emission in star-forming galaxies. We analyze the XMM-Newton/reflection grating spectrometer (RGS) spectrum of M82 using a newly developed CX model combined with a single-temperature thermal plasma to characterize the volume-filling hot gas. The CX process is largely responsible for not only the strongly enhanced forbidden lines of the Kα triplets of various He-like ions but also good fractions of the Lyα transitions of C vi (∼87%), O viii, and N vii (≳50%) as well. In total about a quarter of the X-ray flux in the RGS 6–30 Å band originates in the CX. We infer an ion incident rate of 3 × 1051 s−1 undergoing CX at the hot and cool gas interface and an effective area of the interface of ∼2 × 1045 cm2 that is one order of magnitude larger than the cross section of the global biconic outflow. With the CX contribution accounted for, the best-fit temperature of the hot gas is 0.6 keV, and the metal abundances are approximately solar. We further show that the same CX/thermal plasma model also gives an excellent description of the EPIC-pn spectrum of the outflow Cap, projected at 11.6 kpc away from the galactic disk of M82. This analysis demonstrates that the CX is potentially an important contributor to the X-ray emission from starburst galaxies and also an invaluable tool to probe the interface astrophysics.