Tracing the formation of molecular clouds via [C ii], [C i], and CO emission
Tracing the formation of molecular clouds via [C ii], [C i], and CO emission
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DOI：
10.1093/mnras/stz1119
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发表时间：
2018-09
影响因子：
4.8
通讯作者：
P. Clark;S. Glover;S. Ragan;A. Duarte-Cabral
中科院分区：
文献类型：
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作者：
P. Clark;S. Glover;S. Ragan;A. Duarte-Cabral
如果我们有一个可靠的观测示踪剂来追踪形成云的气体流动，我们对星际介质中分子云形成的理解将大有帮助。单电离和中性碳（[C ii]，[C i]）的精细结构发射和CO的转动谱线发射都与分子云有关。然而，目前还不清楚这些示踪剂是否可以用来研究气体流入到正在聚集的云上，或者它们是否主要追踪已经聚集的云。在本文中，我们解决这个问题的帮助下，高分辨率的模拟分子云的形成，包括一个复杂的治疗的化学和热物理的ISM。我们的模拟表明，[C i]和CO排放的痕量气体主要是分子，密度为500-1000 cm−3，远大于流入气体的密度。[C ii]是低密度物质（n = 100 cm−3）的痕迹，在早期主要是原子。大部分的[C ii]排放跟踪相同的结构作为[C i]或CO排放，但一些出现在流入的气体。不幸的是，这种辐射非常微弱，用现有的观测设施很难探测到，即使是位于星际辐射场升高的区域的云。
Our understanding of how molecular clouds form in the interstellar medium (ISM) would be greatly helped if we had a reliable observational tracer of the gas flows responsible for forming the clouds. Fine structure emission from singly ionized and neutral carbon ([C ii], [C i]) and rotational line emission from CO are all observed to be associated with molecular clouds. However, it remains unclear whether any of these tracers can be used to study the inflow of gas on to an assembling cloud, or whether they primarily trace the cloud once it has already assembled. In this paper, we address this issue with the help of high-resolution simulations of molecular cloud formation that include a sophisticated treatment of the chemistry and thermal physics of the ISM. Our simulations demonstrate that both [C i] and CO emission trace gas that is predominantly molecular, with a density n ∼ 500–1000 cm−3, much larger than the density of the inflowing gas. [C ii] traces lower density material (n ∼ 100 cm−3) that is mainly atomic at early times. A large fraction of the [C ii] emission traces the same structures as the [C i] or CO emission, but some arises in the inflowing gas. Unfortunately, this emission is very faint and will be difficult to detect with current observational facilities, even for clouds situated in regions with an elevated interstellar radiation field.