从星系团、星系群和椭圆星系的叠加X射线光栅谱揭示O VII
Revealing O VII from stacked X-ray grating spectra of clusters, groups and elliptical galaxies
摘要：
我们堆叠4.6兆的高光谱分辨率XMM-牛顿反射光栅光谱仪光谱从星系团，星系群和椭圆星系。对于那些中心温度小于1 keV的天体，我们首次探测到O VII，错误探测的概率为2.5x10^-4。O VII与Fe XVII谱线的通量比是在没有加热的情况下等压辐射冷却所预期的发射的1/4到1/8。存在防止冷却到0.5 keV以下的过程、反常的O/Fe丰度比、在最冷的X射线发射气体周围的吸收材料或发生非辐射冷却。平均N VII发射线在亚keV样品中是强的。由于类氢N和O线的比率在很大程度上与温度无关，我们测量到平均N/O比率为4.0 +- 0.6太阳能。虽然C VI线周围的连续谱很难测量，但我们可以类似地估计C/O比为0.9 +- 0.3太阳能。
英文摘要：
We stack 4.6 Ms of high spectral resolution XMM-Newton Reflection Grating Spectrometer spectra from galaxy clusters, groups of galaxies and elliptical galaxies. For those objects with a central temperature of less than 1 keV, we detect O VII for the first time, with a probability of false detection of 2.5x10^-4. The flux ratio of the O VII to Fe XVII lines is 1/4 to 1/8 of the emission expected for isobaric radiative cooling in the absence of heating. There is either a process preventing cooling below 0.5 keV, anomalous O/Fe abundance ratios, absorbing material around the coolest X-ray emitting gas or non-radiative cooling taking place. The mean N VII emission line is strong in the sub-keV sample. As the ratio of the hydrogenic N and O lines is largely independent of temperature, we measure a mean N/O ratio of 4.0 +- 0.6 Solar. Although the continuum around the C VI lines is difficult to measure we can similarly estimate that the C/O ratio is 0.9 +- 0.3 Solar.
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