一个H $α$ /X射线孤云作为团内介质成团的标志
An H$α$/X-ray orphan cloud as a signpost of the intracluster medium clumping
摘要：
最近的研究强调了团内介质（ICM）凝聚的潜在意义及其对团宇宙学和重子物理的重要意义。许多ICM团块可能起源于下落星系，因为剥离的星际介质（ISM）混合到热ICM中。然而，ICM聚集和剥离ISM之间的直接联系以前没有明确建立。在这里，我们提出了第一个也是唯一已知的孤立云（或孤儿云，OC）在附近的集群阿贝尔1367中的X射线和H $α$检测到的发现。有效半径为30千秒差距，该云的平均X射线温度为1.6千电子伏，辐射热X射线光度为$\sim 3.1\times 10^{41}$ erg s $^{-1}$，热气质量为$\sim 10^{10}\ {\rm M}_\odot$。根据MUSE数据，OC显示出几乎沿东西方向的有趣的速度梯度，具有$\sim 80$ km/s的低水平速度分散，这可能表明ICM湍流水平较低。发射谱线的诊断表明，在主H $α$云和一个LI（N）ER光谱中几乎没有恒星形成，但激发机制仍不清楚。这个例子表明，剥离的ISM，即使在最初从星系中移除很长一段时间后，仍然可以引起ICM的不均匀性。我们认为，磁场可以通过抑制流体动力学不稳定性和热传导来稳定OC。该实施例还表明，至少一些ICM团块在性质上是多相的，并且暗示ICM团块也可以在H $α$中被追踪。因此，未来的深场和宽场H $α$调查可以用来探测ICM聚集和湍流。
英文摘要：
Recent studies have highlighted the potential significance of intracluster medium (ICM) clumping and its important implications for cluster cosmology and baryon physics. Many of the ICM clumps can originate from infalling galaxies, as stripped interstellar medium (ISM) mixing into the hot ICM. However, a direct connection between ICM clumping and stripped ISM has not been unambiguously established before. Here we present the discovery of the first and still the only known isolated cloud (or orphan cloud, OC) detected in both X-rays and H$α$ in the nearby cluster Abell 1367. With an effective radius of 30 kpc, this cloud has an average X-ray temperature of 1.6 keV, a bolometric X-ray luminosity of $\sim 3.1\times 10^{41}$ erg s$^{-1}$ and a hot gas mass of $\sim 10^{10}\ {\rm M}_\odot$. From the MUSE data, the OC shows an interesting velocity gradient nearly along the east-west direction with a low level of velocity dispersion of $\sim 80$ km/s, which may suggest a low level of the ICM turbulence. The emission line diagnostics suggest little star formation in the main H$α$ cloud and a LI(N)ER-like spectrum, but the excitation mechanism remain unclear. This example shows that the stripped ISM, even long time after the initial removal from the galaxy, can still induce the ICM inhomogeneities. We suggest that magnetic field can stabilize the OC by suppressing hydrodynamic instabilities and thermal conduction. This example also suggests that at least some ICM clumps are multi-phase in nature and implies that the ICM clumps can also be traced in H$α$. Thus, future deep and wide-field H$α$ survey can be used to probe the ICM clumping and turbulence.
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