X射线苏黎世环境研究（X-ZENS）。II。星系群内弥散介质的X射线观测
The X-Ray Zurich Environmental Study (X-ZENS). II. X-ray Observations of the Diffuse Intragroup Medium in Galaxy Groups
摘要：
我们提出了一个试点$Newton$和$Chandra$计划的结果，旨在研究从2010年环境研究（ZENS）目录中光学选择的邻近群体的弥散性群体内介质（DIM）。这些星系群的质量范围很窄，大约是$10^{13}M_\odot$，在这个质量范围内，DIM和星系群成员星系之间的相互作用在很大程度上还没有被探测到。DIM的X射线发射在0.5- 2 keV的能带中被探测到，通量为$\le 10^{-14}$ erg cm $^{-1}$ s $^{-1}$，比典型的ROSAT群（RASS）弱一个数量级。对于许多组，我们为X射线亮度设置了上限，这表明探测可能探测到了X射线发射组的上限。我们发现的证据，我们的光学选择的群体是根据发光相对于预测从X射线标度关系。X射线质量的测定与基于成员星系的膨胀光度，其次是它们的总光学光度和速度色散的最佳协议。我们测量的恒星质量分数的中值约为1 $\%$，与来自最大质量的星系之间的30至50%的贡献。光学和X射线数据往往提供互补的答案有关的动态状态的集团，是必不可少的一个完整的图片系统。将这一试点计划扩展到更大的群体样本是强制性的，以揭示成员星系和DIM之间相互作用的任何印记，这对环境驱动的星系演化至关重要。
英文摘要：
We present the results of a pilot XMM-$Newton$ and $Chandra$ program aimed at studying the diffuse intragroup medium (DIM) of optically-selected nearby groups from the Zurinch ENvironmental Study (ZENS) catalog. The groups are in a narrow mass range about $10^{13}M_\odot$, a mass scale at which the interplay between the DIM and the group member galaxies is still largely unprobed. X-ray emission from the DIM is detected in the energy band 0.5--2 keV with flux $\le 10^{-14}$ erg cm$^{-1}$ s$^{-1}$, which is one order of magnitude fainter than for typical ROSAT groups (RASS). For many groups we set upper limits to the X-ray luminosity, indicating that the detections are likely probing the upper envelope of the X-ray emitting groups. We find evidence for our optically selected groups to be under-luminous with respect to predictions from X-ray scaling relations. X-ray mass determinations are in best agreement with those based on the member galaxies bulge luminosity, followed by their total optical luminosity and velocity dispersion. We measure a stellar mass fraction with a median value of about 1$\%$, with a contribution from the most massive galaxies between 30 to 50 \%. Optical and X-ray data give often complementary answers concerning the dynamical state of the groups, and are essential for a complete picture of the system. Extending this pilot program to a larger sample of groups is mandatory to unveil any imprint of interaction between member galaxies and DIM in halo potentials of key importance for environmentally-driven galactic evolution.
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