Abstract

We present observations of the ³P₁–³P₀ fine-structure line of atomic carbon using the ASTE 10m sub-mm telescope towards RCW 38, the youngest super star cluster in the Milky Way. The detected [C i] emission is compared with the CO J = 1–0 image cube presented in Fukui et al. (2016, ApJ, 820, 26) which has an angular resolution of 40^″ (∼0.33 pc). The overall distribution of the [C i] emission in this cluster is similar to that of the ¹³CO emission. The optical depth of the [C i] emission was found to be τ = 0.1–0.6, suggesting mostly optically thin emission. An empirical conversion factor from the [C i] integrated intensity to the H₂ column density was estimated as X_[C i]$= 6.3 \times 10 ^{20}\:$cm⁻² K⁻¹ km⁻¹ s (for visual extinction: A_V ≤ 10 mag) and 1.4 × 10²¹ cm⁻² K⁻¹ km⁻¹ s (for A_V of 10–100 mag). The column density ratio of the [C i] to CO (N_[C i]$/N_{\rm CO}$) was derived as ∼0.1 for A_V of 10–100 mag, which is consistent with that of the Orion cloud presented in Ikeda et al. (2002, ApJ, 571, 560). However, our results cover an A_V regime of up to 100 mag, which is wider than the coverage found in Orion, which reaches up to ∼60 mag. Such a high [C i]$/$CO ratio in a high-A_V region is difficult to explain via the plane-parallel photodissociation region model, which predicts that this ratio is close to 0 due to the heavy shielding of the ultraviolet (UV) radiation. Our results suggest that the molecular gas in this cluster is highly clumpy, allowing deep penetration of UV radiation even at averaged A_V values of 100 mag. Recent theoretical works have presented models consistent with such clumped gas distribution with a sub-pc clump size (e.g., Tachihara et al. 2018, arXiv:1811.02224).

中文翻译：

---

[Ci]（3P1–3P0）向大质量恒星形成区域RCW 38发射的观测：分子气体高度聚集的密度分布的进一步证据

摘要

我们使用ASTE 10m亚毫米望远镜朝着RCW 38（银河系中最年轻的超级星团）展示了原子碳的³ P ₁ – ³ P ₀精细结构线的观测结果。将检测到的[C  i ]发射与Fukui等人提出的CO J = 1-0影像立方体进行比较。（2016，ApJ，820，26 ），其角分辨率为40^英寸（〜0.33 pc）。[C i ]排放的总体分布 与¹³ CO排放相似。[C i的光学深度 ]发射被发现为τ= 0.1-0.6，这表明主要是光学上稀薄的发射。从[C i ]积分强度到H ₂柱密度的经验转换因子 估计为X _{[C  i ]} $ = 6.3 \ times 10 ^ {20} \：$ cm ^-2  K ^-1  km ^-1  s（为视觉消光：甲_V ≤10 MAG）和1.4×10 ²¹ 厘米^-2  ķ ^-1 千米^-1  s（对于阿_V 10-100 MAG的）。[C i ]与CO的柱密度比 （N _{[C  i ]}$ / N _ {\ rm CO} $）对于10–100 mag的A _V推导为〜0.1 ，这与Ikeda等人提出的Orion云的一致。（2002，ApJ，571，560）。但是，我们的结果涵盖了高达100 mag的A _V范围，这比Orion的〜60 mag的覆盖范围要宽。很难通过平面平行光解离区域模型来解释高A _V区中如此高的[C  i ] $ / $ CO比，该模型预测由于紫外线的强烈屏蔽，该比值接近于0（紫外线辐射。我们的结果表明，该簇中的分子气体高度结块，即使在平均A _V时也能使UV辐射深入渗透值100磁 最近的理论工作已经提出了与这种具有亚PC团块尺寸的团块气体分布相一致的模型（例如Tachihara等人2018，arXiv：1811.02224）。