星系风的X射线辐射的起源

Properties of hot gas outflows (superwinds) from galaxies are generally measured from associated X-ray line emission assuming that it represents atomic transitions in thermally excited hot gas. X-ray line emission, however, can also arise from the charge exchange between highly ionized ions and neutral species, which has been used to explain the bright X-ray emission observed in comets. Recently, we found that the OVII Kα triplets of the superwinds of nearby starburst galaxies (including M82 and NGC253, resolved by XMM-Newton RGS) are dominated by the forbidden line, which is consistent with the charge exchange X-ray emisson rather than the thermal model. This has strong implications for our understanding of the properties (metal, mass, and energy) of the superwind, which is an important feedback process regulating the evolution of galaxies. It is crucial to determine the origin of the X-ray emission of the superwind. We propose to study the spatial correlation between the X-ray emission and neutral gas to further test the charge exchange mechanism and re-estimate the properties of the galactic superwinds based on the charge exchange model. We will also study the physical implications and other possible observational characteristics produced by the charge exchange process.

最近我们发现近邻星爆星系（包括M82和NGC253等）的星系风的OVII Kα的三重线是由禁线主导的，这与传统的热等离子体辐射模型相悖，而与电荷交换X射线辐射机制相符。电荷交换辐射发生于热的高电离离子与冷的中性原子或分子界面上，是一个极有效的X射线辐射机制，已被用来解释彗星的强X射线辐射。我们的这个发现对理解星系风的物理参数（质量和能量）及其所携带的金属具有重要意义。星系风是控制星系演化的一个主要反馈过程，其性质只有通过它们的X射线辐射才能得以直接测量，因此，正确理解星系风的X射线辐射的起源是了解星系风性质所必需的第一步。我们计划深入研究X射线辐射和冷气体的空间相关性来进一步确认星系风的电荷交换X射线辐射机制，并用电荷交换模型重新估计星系风的相关物理量。我们也将研究热气体与冷气体的电荷交换作用可能导致的物理效应及其它的观测特征。

我们研究了星系风X射线辐射的机制问题，关注于X射线波段的OVII 三重线和其在光学波段的观测特征。我们在M51核区的Chandra能谱上探测到了一系列的非铁的荧光线，包括Si, S, Ar, Ca, Cr, 和 Mn。我们意识到非铁的荧光线是一个新的可以用来研究活动星系核区尘埃环的工具。我们测量了10个II 型活动星系核的Fe Ka/Si Ka 的线比率，结果表明其尘埃环都是块状分布的，而不是连续分布的。我们测量了Circinus, Mrk 3, 和NGC 1068的Si Ka 的线宽，其值约为500 km/s，这使得其荧光线发射区距离放大到尘埃蒸发半径的外面，不同于以前基于Fe Ka 线宽对发射区距离的估计。