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arXiv 1902.03733astro-ph.GA
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天炉座星团内X射线源的Chandra探测

Chandra Detection of Intra-cluster X-ray Sources in Fornax

Xiangyu Jin, Meicun Hou, Zhenlin Zhu, Zhiyuan Li

摘要:

基于总曝光量为1.3 Ms的{ \it Chandra}观测资料,我们研究了天炉座星系团中的X射线点源,主要目的是寻找星系团内的X射线源群。我们探测到1177个点源,从星团中心到$\sim$ 30弧分($\sim$ 180千秒差距)的投影半径,并下降到$\sim3\times10^{37}{\rm~erg~s^{-1}}$的极限0.5- 8千电子伏的光度。在排除了与前景星、已知球状星团、超致密矮星和星系核有关的源后,我们构造了源面密度剖面。从这个配置文件中,我们统计识别$\sim$ 183多余的来源,不与个别成员星系的天炉座的散装恒星内容,也不与宇宙X射线背景。在考虑泊松误差和宇宙方差的情况下,在中心巨椭圆NGC 1,1399的三个有效半径之外,这种过剩的累积显著性处于$\gtrsim 2\,σ$水平(最大值为3.6\,$σ$).多余的源的光度函数被发现是显着陡峭的GC托管源(大概是低质量的X射线双星[LMXB]),不利的可能性,身份不明的GC是主要负责的过剩。我们发现,大部分的过剩可以与扩展的恒星晕的NGC 1399和/或弥漫的星系团内的光,从而提供了强有力的证据,在天炉座,第二个明确的情况下,一个星系团后室女座星系团内的X射线源的存在。其他可能的起源过剩,包括超新星踢LMXB和剥离有核矮星系进行了讨论。

英文摘要:

Based on archival {\it Chandra} observations with a total exposure of 1.3 Ms, we study X-ray point sources in the Fornax cluster of galaxies, with the primary aim of searching for intra-cluster X-ray source populations. We detect 1177 point sources out to a projected radius of $\sim$30 arcmin ($\sim$180 kpc) from the cluster center and down to a limiting 0.5--8 keV luminosity of $\sim3\times10^{37}{\rm~erg~s^{-1}}$. We construct source surface density profile, after excluding sources associated with foreground stars, known globular clusters, ultra-compact dwarfs and galactic nuclei. From this profile we statistically identify $\sim$183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax, nor with the cosmic X-ray background. Taking into account Poisson error and cosmic variance, the cumulative significance of this excess is at $\gtrsim 2\,σ$ level (with a maximum of 3.6\,$σ$) outside three effective radii of the central giant elliptical, NGC\,1399. The luminosity function of the excess sources is found to be significantly steeper than that of the GC-hosting sources (presumably low-mass X-ray binaries [LMXBs]), disfavoring the possibility that unidentified GCs are primarily responsible for the excess. We show that a large fraction of the excess can be related to the extended stellar halo of NGC\,1399 and/or the diffuse intra-cluster light, thus providing strong evidence for the presence of intra-cluster X-ray sources in Fornax, the second unambiguous case for a galaxy cluster after Virgo. Other possible origins of the excess, including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed.

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