超软X射线源在不同形态星系中的粒子数
Populations of super-soft X-ray sources in galaxies of different morphological types
摘要：
我们研究人口的软和超软X射线源在附近的各种形态类型的星系，特别强调稳定的核燃烧吸积WD人口的特征。通过分析钱德拉档案的内容，我们收集了一个适合研究超软X射线源种群的邻近星系样本。我们的样本包括4个旋涡星系、2个透镜星系和3个椭圆星系，它们的恒星质量超过$10^{10}$ $M_\odot$，X射线灵敏度为${\rm few}\times 10^{36}$ erg/s。我们采用硬度比和中值能量相结合的方法对软谱X射线源进行预选，并利用温度-X射线光度图对超软X射线源--可能的核燃烧吸积白矮星进行识别。对于螺旋星系来说，有一个独特且罕见的超软源群，它们很大程度上与$kT_{bb}-L_X$平面上的其他源分离。这些源和数量更多的硬（但仍然软）源之间的边界与白矮星表面稳定氢燃烧的边界一致。位于该边界外的软源的组合谱显示出清晰的Mg和S发射线，其等效宽度与M83中大量已确认超新星遗迹的组合谱相似。这证实了先前的建议，即绝大多数所谓的准软源是超新星遗迹。在早型星系中，超软源的数量大约是$\approx 8$的一个因子，与人口合成计算结果基本一致。超软源的具体频率为：旋涡星系中的（2.08 PDMATHAMR 0.46）$\times10^{-10}$ M PDMATHAMT，透镜星系和椭圆星系中的（2.47 PDMATHAMR 1.34）$\times10^{-11}$ M $_{\odot}^{-1}$，后者与前者的比值为$0.12\pm0.05$。
英文摘要：
We study populations of soft and super-soft X-ray sources in nearby galaxies of various morphological types with the special emphasis on characterizing populations of stable nuclear burning accreting WDs. Analysing the content of Chandra archive we assembled a sample of nearby galaxies suitable for studying populations of super-soft X-ray sources. Our sample includes 4 spiral galaxies, 2 lenticular galaxies and 3 ellipticals with stellar mass exceeding $10^{10}$ $M_\odot$ and X-ray sensitivity of the order of a ${\rm few}\times 10^{36}$ erg/s. We used combination of hardness ratio and median energy to pre-select X-ray sources with soft spectra, and temperature - X-ray luminosity diagram to identify super-soft X-ray sources - likely nuclear burning accreting white dwarfs. For spiral galaxies, there is a distinct and rare population of super-soft sources, largely detached from the rest of sources on the $kT_{bb}-L_X$ plane. The boundary between these sources and the much more numerous population of harder (but still soft) sources is consistent with the boundary of stable hydrogen burning on the white dwarf surface. Combined spectrum of soft sources located outside this boundary, shows clear emission lines of Mg and S, which equivalent width is similar to that in the combined spectrum of a large number of confirmed supernova remnants in M83. This confirms earlier suggestions that the vast majority of so called quasi-soft sources are supernova remnants. In early-type galaxies, populations of super-soft sources are about a factor of $\approx 8$ less abundant, in broad agreement with the population synthesis calculations. Specific frequencies of super-soft sources are: (2.08$\pm$0.46)$\times10^{-10}$ M$_{\odot}^{-1}$ in spiral galaxies and (2.47$\pm$1.34)$\times10^{-11}$ M$_{\odot}^{-1}$ in lenticular and elliptical galaxies, with the ratio of the latter to the former of $0.12\pm0.05$.
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