论文标题
不同形态类型的星系中的超软X射线源的种群
Populations of super-soft X-ray sources in galaxies of different morphological types
论文作者
论文摘要
我们研究了各种形态类型的附近星系中软柔软的X射线源的种群，特别着重于表征稳定的核燃烧增值WD的种群。分析钱德拉档案馆的内容，我们组装了一个适合研究超柔软X射线源种群的附近星系样本。我们的样本包括4个螺旋星系，2个宽带星系和3个椭圆形，其恒星质量超过$ 10^{10} $ $ M_ \ odot $和X射线敏感性，$ {\ rm少数几个} \ times 10^{36} $ erg/s的顺序。我们使用硬度比和中值能量的组合来预选X射线源，并具有软光谱和温度 - X射线光度图来识别超柔软的X射线源 - 可能会积聚白矮人的核燃烧。对于螺旋星系，有一个独特且罕见的超柔软来源，在$ kt_ {bb} -l_x $ plane上的其余来源基本上分离出来。这些来源与更多的硬源（但仍然软）的数量群体之间的边界与白色矮人表面上稳定的氢燃烧的边界是一致的。位于该边界之外的软源的组合频谱显示了Mg和S的清晰发射线，等效宽度与M83中大量确认的超新星残留物的合并频谱相似。这证实了以前的建议，即绝大多数所谓的准柔软来源都是超新星残留物。在早期类型的星系中，超柔软来源的种群约为$ \ 8 $少，与人口综合计算相吻合。超柔软来源的特定频率为：（2.08 $ \ pm $ 0.46）$ \ times10^{ - 10} $ m $ $ _ {\ odot}^{ - 1} $在螺旋星系中和（2.47 $ \ pm $ 1.34）椭圆星系，后者与前者的比率为0.12美元\ pm0.05 $。
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 $0.12\pm0.05$.
