论文标题
M51中央区域电荷交换的光谱模型
Spectral Modeling of Charge Exchange in the Central Region of M51
论文作者
论文摘要
电荷交换（CX）发射揭示了星系的密集，多相，周环区域的中性和离子化星间培养基（ISM）组件之间的显着相互作用。我们使用包括热和CX组件在内的模型来描述M51中央区域中弥漫发射的高分辨率XMM-Newton/RGS光谱。该模型可以很好地解释CX发射的代表性签名 - 尤其是OVII的突出OVII禁止线和OVIII ly $γ$线中的过量发射 - 该模型可以很好地解释。结合OVIII和OVII带中的Chandra图像，我们发现软X射线发射由喷射驱动的流出及其与环境中性材料的相互作用所支配。喷射驱动的流出本身可能是$ \ sim 0.59 $ keV的热等离子体，其中大部分是亚极性的。它进入环境中性气体，并产生明显的CX发射，占7---28Å频段中弥漫性X射线发射的五分之一。 CX过程中的有效界面区域比喷气驱动流出的几何表面积大的数量级。由核恒星形成驱动的脆弱流出也可能对弥漫性热和CX发射造成很小的一部分。活跃银河核（AGN）的光电离是热气体本身的谐振散射，尽管不排除过去AGN事件的影响。
Charge exchange (CX) emission reveals the significant interaction between neutral and ionized interstellar medium (ISM) components of the dense, multiphase, circumnuclear region of a galaxy. We use a model including a thermal and a CX components to describe the high-resolution XMM-Newton/RGS spectrum of the diffuse emission in the central region of M51. Representative signatures of CX emission -- especially the prominent OVII forbidden line and the excess emission in the OVIII Ly$γ$ lines -- can be well explained by the model. Combined with the Chandra images in the OVIII and the OVII bands, we find the soft X-ray emission is dominated by the jet-driven outflow and its interaction with the ambient neutral material. The jet-driven outflow itself is likely a thermal plasma of $\sim 0.59$ keV, with mostly sub-solar abundances. It runs into the ambient neutral gas, and produces significant CX emission that accounts for one-fifth of the diffuse X-ray emission in the 7--28 Å band. The effective interface area in the CX process is one order of magnitude greater than the geometrical surface area of the jet-driven outflow. The tenuous outflow driven by the nuclear star formation may also contribute a small portion to both the diffuse thermal and CX emission. The photoionization by the active galactic nuclei (AGNs) and the resonance scattering by the hot gas itself are disfavored, though the effects from past AGN events may not be ruled out.
