Synthetic [C ii] emission maps of a simulated molecular cloud in formation
Synthetic [C ii] emission maps of a simulated molecular cloud in formation
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DOI：
10.1093/mnras/sty2507
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发表时间：
2018-09
影响因子：
4.8
通讯作者：
A. Franeck;S. Walch;D. Seifried;S. Clarke;V. Ossenkopf-Okada;S. Glover;R. Klessen;P. Girichidis;T. Naab;R. Wünsch;P. Clark;E. Pellegrini;T. Peters
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文献类型：
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作者：
A. Franeck;S. Walch;D. Seifried;S. Clarke;V. Ossenkopf-Okada;S. Glover;R. Klessen;P. Girichidis;T. Naab;R. Wünsch;P. Clark;E. Pellegrini;T. Peters
C+离子是星际气体的重要冷却剂，因此[C ii]精细结构线在星际介质中经常被观测到。然而，[C ii]排放气体的物理和化学性质仍不清楚。我们进行非LTE辐射传输模拟与radmc-3d研究的[C ii]线发射从一个年轻的，动荡的分子云开始之前的星星形成，使用的数据从SILCC-Zoom项目。[C ii]发射的光学厚度超过40%的可观测区域，I[CII] > 0.5 K km s−1。为了确定[C ii]发射气体的物理性质，我们将[C ii]发射视为光学薄。我们发现[C ii]发射主要来自冷的中等密度气体（40 <$T <$65 K和50 <$n <$440 cm−3），主要由氢原子组成，有效的视觉消光在10.50和10.91之间。以分子氢为主的气体仅占总[C ii]线发射的约20%。因此，[C二]是不是一个很好的示踪剂CO暗H2在这个早期阶段的云的生命。我们还发现，总气体，H和C+柱密度都与集成[C II]线发射，与幂律斜率范围从0.5到0.7。此外，总柱密度和[C ii]线发射之间的中值比为YCII = 1.1 × 1021 cm−2（K km s−1）−1，YCII的标度为I −0.3 [CII] I[CII]−0.3。我们预计YCII将在比这里模拟的辐射场更低或更高的环境中发生变化。
The C+ ion is an important coolant of interstellar gas, and so the [C ii] fine structure line is frequently observed in the interstellar medium. However, the physical and chemical properties of the [C ii]-emitting gas are still unclear. We carry out non-LTE radiative transfer simulations with radmc–3d to study the [C ii] line emission from a young, turbulent molecular cloud before the onset of star formation, using data from the SILCC-Zoom project. The [C ii] emission is optically thick over 40% of the observable area with I[CII] > 0.5 K km s−1. To determine the physical properties of the [C ii] emitting gas, we treat the [C ii] emission as optically thin. We find that the [C ii] emission originates primarily from cold, moderate density gas (40 ≲ T ≲ 65 K and 50 ≲ n ≲ 440 cm−3), composed mainly of atomic hydrogen and with an effective visual extinction between ∼0.50 and ∼0.91. Gas dominated by molecular hydrogen contributes only ≲20% of the total [C ii] line emission. Thus, [C ii] is not a good tracer for CO-dark H2 at this early phase in the cloud’s lifetime. We also find that the total gas, H and C+ column densities are all correlated with the integrated [C ii] line emission, with power law slopes ranging from 0.5 to 0.7. Further, the median ratio between the total column density and the [C ii] line emission is YCII ≈ 1.1 × 1021 cm−2 (K km s−1)−1, and YCII scales with I −0.3 [CII] I[CII]−0.3 . We expect YCII to change in environments with a lower or higher radiation field than simulated here.