AI 中文总结
本研究利用JWST观测分析z=7.88处原星系团A2744-z7p9OD的23个成员星系，发现恒星质量等性质与全局环境指标强相关，核心区富含中性气体、电离光子逃逸受抑制，为早期星系环境演化及再电离研究提供了观测依据。
AI 中文摘要
再电离时期的原星系团是探究环境如何塑造早期星系形成与演化的关键实验室，也可能对宇宙再电离有所贡献。我们利用JWST（詹姆斯·韦布空间望远镜）的NIRCam（近红外相机）和NIRSpec（近红外光谱仪），分析了红移$z=7.88$的原星系团A2744-z7p9OD的23个成员星系，研究其恒星族性质、静止系紫外尺寸以及电离气体性质。我们还分别以到质量最大星系的投影距离（$D_{\rm YD4}$）作为全局环境指标、到最近邻星系的投影距离（$D_{\rm nei}$）作为局地环境指标，量化了A2744-z7p9OD的内部结构。恒星质量、100 Myr时标下的恒星形成率（SFR）、尘埃消光以及星系尺寸均与$D_{\rm YD4}$呈现显著相关性（$p<0.05$），但与$D_{\rm nei}$无相关性，表明这些性质主要与原星系团的全局结构相关。成员星系的R23（定义为$\boldsymbol{\rm \boldsymbol{\textit{R23}}=\boldsymbol{\rm \boldsymbol{\textit{log}}(([\boldsymbol{\rm O\textsc{iii}}]\boldsymbol{\rm \boldsymbol{\textit{λ}}}\boldsymbol{\rm \boldsymbol{\textit{λ}}}4960,5008\boldsymbol{\rm \boldsymbol{\textit{Å}}}+[\boldsymbol{\rm O\textsc{ii}}]\boldsymbol{\rm \boldsymbol{\textit{λ}}}\boldsymbol{\rm \boldsymbol{\textit{λ}}}3727,3730\boldsymbol{\rm \boldsymbol{\textit{Å}}})/\boldsymbol{\rm H}\boldsymbol{\rm \boldsymbol{\textit{β}}})}}$）存在较大的星系间差异，暗示原星系团环境中的化学增丰是不均匀的。O32（定义为$\boldsymbol{\rm \boldsymbol{\textit{O32}}=\boldsymbol{\rm \boldsymbol{\textit{log}}}([\boldsymbol{\rm O\textsc{iii}}]\boldsymbol{\rm \boldsymbol{\textit{λ}}}5008\boldsymbol{\rm \boldsymbol{\textit{Å}}}/[\boldsymbol{\rm O\textsc{ii}}]\boldsymbol{\rm \boldsymbol{\textit{λ}}}\boldsymbol{\rm \boldsymbol{\textit{λ}}}3727,3730\boldsymbol{\rm \boldsymbol{\textit{Å}}})}$）与$D_{\rm YD4}$相关，表明原星系团核心区域的气体电离度较低。结合Lyα发射线未被探测到、ALMA（阿塔卡马大型毫米/亚毫米波阵列）的[C ii] 158μm发射线所指示的可能中性气体储库，以及核心区存在高柱密度中性氢的证据，这些结果表明该原星系团核心富含中性气体，即便处于再电离时期（EoR）的过密环境中，当前电离光子的逃逸也可能受到抑制。
英文摘要
Protoclusters in the epoch of reionization provide key laboratories for investigating how environment shapes early galaxy formation and evolution, and may also have contributed to cosmic reionization. We analyze 23 member galaxies of A2744-z7p9OD, a protocluster at $z=7.88$, using JWST/NIRCam and NIRSpec to investigate their stellar population properties, rest-frame UV sizes, and ionized-gas properties. We also quantify the internal structure of A2744-z7p9OD using the projected distance to the most massive galaxy ($D_{\rm YD4}$), and to the nearest neighbor ($D_{\rm nei}$), as global and local environmental indicators, respectively. Stellar mass, SFR on a 100 Myr timescale, dust attenuation, and galaxy size show significant correlations ($p<0.05$) with $D_{\rm YD4}$, but not with $D_{\rm nei}$, suggesting that these properties are primarily linked to the global protocluster structure. The member galaxies also show a large galaxy-to-galaxy variation in R23 ($=\log{(([\mathrm{O}\text{\textsc{iii}}]λ\lambda4960,5008\rmÅ+[\mathrm{O}\text{\textsc{ii}}]λ\lambda3727,3730\rmÅ)/\rm{H}β)}$), implying inhomogeneous chemical enrichment in the protocluster environment. O32 ($=\log{([\mathrm{O}\text{\textsc{iii}}]\lambda5008\rmÅ/[\mathrm{O}\text{\textsc{ii}}]λ\lambda3727,3730\rmÅ)}$) correlates with $D_{\rm YD4}$, indicating that the core region is characterized by low-ionization gas. Together with the non-detection of Ly$α$ emission, the possible neutral-gas reservoir traced by ALMA [C{\sc ii}]~$158μ$m emission, and evidence for high-column-density neutral hydrogen in the core, this suggests a neutral-gas-rich protocluster core where the current escape of ionizing photons may be suppressed, even in a overdense environment during the EoR.
Comments29 pages, 10 figures, 5 tables. Submitted to ApJ. Comments welcome
