宇宙黎明时期的预virialized组装：紧凑群CGG-z7的动力学和极端电离
Pre-Virialized Assembly at Cosmic Dawn: The Dynamics and Extreme Ionization of Compact Group CGG-z7 at $z\sim7.04$
AI总结：
研究发现CGG-z7为宇宙黎明时期预virialized结构，通过光谱分析揭示其极端电离条件和低金属licity，揭示了大规模星系形成过程。
摘要：
我们报告了CGG-z7的发现，这是在GOODS-North区域内发现的最紧凑的星系群，观测由JWST POPPIES计划完成。该系统包含至少六个成员，投影尺寸为7.8×5.7kpc²，其中四个通过[O III]和Hβ发射光谱确认。该群的径向速度弥散较低（约93.7km/s）相对于其显著的恒星质量（M*≈10^9.8M_sun），导致恒星-动力学质量比为M*/M_vir≈0.15。该比值超过典型virialized晕值3倍，表明该系统很可能不在动态平衡中。相反，我们将CGG-z7解释为预virialized结构，可能是处于近apocenter的主合并体——捕捉到大规模“红核”的快速、混沌形成。光谱分析显示该群内存在极端电离条件和低金属licity。特别是，中心星系达到极高的[O III]/Hβ比值约为18，这可能指示了一个被遮蔽的AGN。因此，CGG-z7成为研究预virialized星系组装物理的独特实验室，连接了高红移的湍流组装与宇宙正午时的宁静星系。
英文摘要：
We report the discovery of CGG-z7, the most compact galaxy group at $z\gtrsim7$ identified to the north of the GOODS-North field, observed by the JWST POPPIES program. The system consists of at least six members within a projected size of $7.8\times5.7$ kpc$^2$, four of which are spectroscopically confirmed via [O III] and H$β$ emission. The group exhibits a low line-of-sight velocity dispersion ($\approx93.7$ km s$^{-1}$) relative to its substantial stellar mass ($M_* \approx 10^{9.8} M_{\odot}$), yielding a stellar-to-dynamical mass ratio of $M_*/M_{\mathrm{vir}} \approx 0.15$. This ratio, exceeding typical values for virialized halos by a factor of $3$, indicates that the system is highly likely not in dynamical equilibrium. Instead, we interpret CGG-z7 as a pre-virialized structure, likely a major merger caught near apocenter -- capturing the rapid, chaotic formation of a massive "Red Nugget". Spectroscopic analysis reveals extreme ionization conditions and low metallicity across the group. In particular, the central galaxy reaches an extraordinarily high [O III]/H$β$ ratio of $\sim18$, which is likely indicative of an obscured AGN. CGG-z7 thus serves as a unique laboratory for the physics of pre-virialized galaxy assembly, bridging the gap between turbulent high-$z$ assembly and the quiescent galaxies seen at cosmic noon.
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