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arXiv 1204.0367astro-ph.CO
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塞弗特的六重奏:天然气在哪里?

Seyfert's Sextet: where is the gas?

S. Tamburri, G. Trinchieri, A. Wolter, J. Sulentic, A. Durbala, M. Rosado

摘要:

塞弗特的六重星系(又名HCG 79)是本宇宙中最紧凑和孤立的星系群之一。它显示了一个突出的漫射光分量,占总观测光的约50%。这可能表明该集团正处于高级进化阶段,这将预示着一个重要的热气体成分。以前的X射线观测表明这个系统的光度很低,但不确定性很大,分辨率很差。我们提出的结果,从深(70 ks),高分辨率的钱德拉观测塞弗特的六重奏,要求与分离的X射线发射与个别星系从一个更广泛的星系间的组成部分的目的。我们讨论的空间和光谱特性,这组我们得出的一些类似的系统也研究了在X射线波段。高分辨率的X射线图像表明,大多数探测到的辐射并不是出现在致密星系团中,而是集中在西北方向,与背景星系团相对应。在(0.5-5)keV波段,单独来自该群的辐射总光度约为1x10^40 erg/s。大部分的光度可以归因于星系中的单个光源,只有~2x10^39 erg/s是由气体成分造成的。然而,我们发现,这一组成部分也主要是与个别星系的六重奏,留下很少或根本没有残留在一个真正的IGM组件。塞弗特六重体的漫发射光度极低,可能与它的总质量很小有关。

英文摘要:

Seyfert's Sextet (a.k.a HCG 79) is one of the most compact and isolated galaxy groups in the local Universe. It shows a prominent diffuse light component that accounts for ~50% of the total observed light. This likely indicates that the group is in an advanced evolutionary phase, which would predict a significant hot gaseous component. Previous X-ray observations had suggested a low luminosity for this system, but with large uncertainties and poor resolution. We present the results from a deep (70 ks), high resolution Chandra observation of Seyfert's Sextet, requested with the aim of separating the X-ray emission associated with the individual galaxies from that of a more extended inter-galactic component. We discuss the spatial and spectral characteristics of this group we derive with those of a few similar systems also studied in the X-ray band. The high resolution X-ray image indicates that the majority of the detected emission does not arise in the compact group but is concentrated towards the NW and corresponds to what appears to be a background galaxy cluster. The emission from the group alone has a total luminosity of ~1x10^40 erg/s in the (0.5-5) keV band. Most of the luminosity can be attributed to the individual sources in the galaxies, and only ~2x10^39 erg/s is due to a gaseous component. However, we find that this component is also mostly associated with the individual galaxies of the Sextet, leaving little or no residual in a truly IGM component. The extremely low luminosity of the diffuse emission in Seyfert's Sextet might be related to its small total mass.

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