arXiv 1504.013972015-04astro-ph.COastro-ph.GA

IDCS +3508：$z > 1.5$中最大的星系团

IDCS J1426.5+3508: The Most Massive Galaxy Cluster at $z > 1.5$

Mark Brodwin, Michael McDonald, Anthony H. Gonzalez, S. A. Stanford, Peter R. Eisenhardt, Daniel Stern, Gregory R. Zeimann

备注：: Minor changes to match accepted version, results unchanged; ApJ in press
DOI：: 10.3847/0004-637X/817/2/122

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摘要：

我们提出了一个深（100 ks）钱德拉观测IDCS J1426.5+3508，光谱证实，红外选择星系团在$z = 1.75$。这个星系团是$z > 1.5$目前已知的最大质量的星系团，基于现有的Sunyaev-Zel'dovich（SZ）和引力透镜探测。我们通过各种X射线标度关系，包括$T_X$-M、$f_g$-M、$Y_X$-M和$L_X$-M，证实了这种高质量，从这些不同的方法中发现了质量的紧密分布，跨越M $_{500}$ = 2.3-3.3 $\times 10^{14}$ M $_{\odot}$，具有基于低散射$Y_X$的质量$M_{500,Y_X} = 2.6^{+1.5}_{-0.5} \times 10^{14}$ M $_\odot$。IDCS J1426.5+3508是目前$z > 1.5$上唯一一个存在X射线、SZ和引力透镜质量估计的星系团，这些估计非常吻合。我们发现气体与总质量比的相对紧密的分布，采用来自所有上述指标的总质量，其值范围为$f_{gas,500}$ = 0.087-0.12。我们在该系统的簇内介质（ICM）中未检测到金属，因此将2 $σ$上限设定为$Z(r < R_{500}) < 0.18 Z_{\odot}$。金属丰度的上限表明，该系统可能仍处于富集ICM的过程中。该星团有一个致密的低熵核心，距离X射线质心偏移$\sim$ 30 kpc，这使其成为$z > 1$发现的少数“冷核心”星团之一，也是$z > 1.2$发现的第一个已知的冷核心星团。这个核心与大尺度质心的偏移表明，这个星团最近（$\lesssim$ 5亿年）与另一个大规模系统合并/相互作用。

英文摘要：

We present a deep (100 ks) Chandra observation of IDCS J1426.5+3508, a spectroscopically confirmed, infrared-selected galaxy cluster at $z = 1.75$. This cluster is the most massive galaxy cluster currently known at $z > 1.5$, based on existing Sunyaev-Zel'dovich (SZ) and gravitational lensing detections. We confirm this high mass via a variety of X-ray scaling relations, including $T_X$-M, $f_g$-M, $Y_X$-M and $L_X$-M, finding a tight distribution of masses from these different methods, spanning M$_{500}$ = 2.3-3.3 $\times 10^{14}$ M$_{\odot}$, with the low-scatter $Y_X$-based mass $M_{500,Y_X} = 2.6^{+1.5}_{-0.5} \times 10^{14}$ M$_\odot$. IDCS J1426.5+3508 is currently the only cluster at $z > 1.5$ for which X-ray, SZ and gravitational lensing mass estimates exist, and these are in remarkably good agreement. We find a relatively tight distribution of the gas-to-total mass ratio, employing total masses from all of the aforementioned indicators, with values ranging from $f_{gas,500}$ = 0.087-0.12. We do not detect metals in the intracluster medium (ICM) of this system, placing a 2$σ$ upper limit of $Z(r < R_{500}) < 0.18 Z_{\odot}$. This upper limit on the metallicity suggests that this system may still be in the process of enriching its ICM. The cluster has a dense, low-entropy core, offset by $\sim$30 kpc from the X-ray centroid, which makes it one of the few "cool core" clusters discovered at $z > 1$, and the first known cool core cluster at $z > 1.2$. The offset of this core from the large-scale centroid suggests that this cluster has had a relatively recent ($\lesssim$500 Myr) merger/interaction with another massive system.

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