AI 中文总结
该研究对9个z~5.8-8.3的莱曼断裂星系开展ALMA观测，揭示z≳6星系尘埃温度与金属丰度负相关，其高[O III]/[C II]比值源于更高的电离参数和气体密度。
AI 中文摘要
我们对9个红移5.8<z_spec<8.3的明亮莱曼断裂星系开展了阿塔卡马大型毫米/亚毫米波阵列（ALMA）高频观测分析。样本包含5个新观测的z~6星系，采用Band-9和/或10波段观测，使我们能更精准地约束z≳6星系统计样本中的尘埃温度（T_dust）。我们对z~6-9星系尘埃温度的测量显示，大部分恒星形成星系的平均尘埃温度约为40 K，而3个星系的尘埃温度显著更高（≳60 K）。我们发现尘埃温度与气体相金属丰度之间存在潜在负相关，关系为T_dust∝Z^(-0.50±0.19)，这意味着低金属丰度环境中尘埃遮蔽减少且尘埃加热更高效。在固定金属丰度下，z~0与z~6-9星系的尘埃温度存在系统偏差，我们发现从z~0到z~6-9星系，尘埃温度可由恒星形成率密度（sSFR）和金属丰度（Z）很好地描述，公式为log T_dust=-0.25^(+0.03)_(-0.04)×(log Z - 0.57×log sSFR)+4.88^(+0.47)_(-0.43)。这些观测在获取尘埃连续谱的同时，还覆盖了5个星系的[OI]63μm发射线，该线可示踪致密中性气体。我们发现z≳6星系的[C II]/[OI]比值低于本地样本，这表明在高气体密度下，碰撞去激发会导致[C II]强度降低。结合[OI]、[O III]、[C II]发射线及 cloudy 模型分析，结果显示z≳6星系的电离参数log U_ion~-2，氢原子数密度log n_H[cm^-3]~2.5，其中电离参数比本地样本高约3-10倍，氢原子数密度比本地样本高约2-3倍。这些增强的电离参数与氢原子数密度的组合，自然解释了z≳6处的高[O III]/[C II]比值。
英文摘要
We present an analysis of ALMA high-frequency observations of nine bright Lyman-break galaxies at $5.8<z_{\rm spec}<8.3$. Our sample consists of five galaxies at $z\sim6$ newly observed in Band-9 and/or 10, allowing us to better constrain the dust temperature ($T_{\rm dust}$) in a statistical sample of $z\gtrsim6$ galaxies. Our measurements of the dust temperature at $z\sim6-9$ suggest most of the star-forming galaxies show $T_{\rm dust}\sim40\,{\rm K}$ on average, whereas three galaxies show significantly higher $T_{\rm dust}$ ($\gtrsim60\,{\rm K}$). We find a potential negative correlation between $T_{\rm dust}$ and gas-phase metallicity with $T_{\rm dust}\propto Z^{-0.50\pm0.19}$, implying decreased dust shielding and efficient dust heating in low-metallicity environments. Given the systematic offset of $T_{\rm dust}$ between $z\sim0$ and $z\sim6-9$ at fixed metallicity, we find $T_{\rm dust}$ is well described by sSFR as well as $Z$ with $\log T_{\rm dust}=-0.25^{+0.03}_{-0.04}\times(\log Z-0.57\times\log {\rm sSFR})+4.88^{+0.47}_{-0.43}$ across $z\sim0$ to $z\sim6-9$. Simultaneously with the dust continuum, these observations cover the [OI]63$μ$m emission line for five galaxies, which traces dense neutral gas. We find a lower [CII]/[OI] ratio in $z\gtrsim6$ galaxies than in local samples, suggesting that [CII] becomes fainter due to collisional de-excitation at high gas density. Combining the [OI], [OIII], and [CII] lines and cloudy modeling, our results imply $\log U_{\rm ion}\sim-2$ and $\log n_{\rm H}\,[{\rm cm}^{-3}]\sim2.5$ in $z\gtrsim6$ galaxies, which is $\sim3-10\times$ higher $U_{\rm ion}$ and $\sim2-3\times$ higher $n_{\rm H}$ than the local samples. The combination of these enhanced $U_{\rm ion}$ and $n_{\rm H}$ naturally explains the high [OIII]/[CII] ratio at $z\gtrsim6$.
