Title: The IRAM-30m line survey of the Horsehead PDR: I. CF+ as a tracer of C+ and a measure of the Fluorine abundance Show Chinese title

Title: IRAM-30米望远镜对马头星云PDR的线谱巡天：I. CF+作为C+的示踪剂及氟丰度的测定

Abstract: C+ is a key species in the interstellar medium but its 158 {\mu}m fine structure line cannot be observed from ground-based telescopes. Current models of fluorine chemistry predict that CF+ is the second most important fluorine reservoir, in regions where C+ is abundant. We detected the J = 1-0 and J = 2-1 rotational lines of CF+ with high signal-to-noise ratio towards the PDR and dense core positions in the Horsehead. Using a rotational diagram analysis, we derive a column density of N(CF+) = (1.5 - 2.0) \times 10^12 cm^-2. Because of the simple fluorine chemistry, the CF+ column density is proportional to the fluorine abundance. We thus infer the fluorine gas-phase abundance to be F/H = (0.6 - 1.5) \times 10^-8. Photochemical models indicate that CF+ is found in the layers where C+ is abundant. The emission arises in the UV illuminated skin of the nebula, tracing the outermost cloud layers. Indeed, CF+ and C+ are the only species observed to date in the Horsehead with a double peaked line profile caused by kinematics. We therefore propose that CF+, which is detectable from the ground, can be used as a proxy of the C+ layers. Show Chinese abstract

Abstract: C+ 是星际介质中的一个关键物种，但其 158 {\mu }m 细结构线无法从地面望远镜观测到。 当前的氟化学模型预测，在 C+ 富集的区域，CF+ 是第二重要的氟储存库。 我们在马头星云的 PDR 和密集核心位置检测到了 CF+ 的 J = 1-0 和 J = 2-1 转动线，且具有高信噪比。 通过转动图分析，我们得出 CF+ 的柱密度为 N(CF+) = (1.5 - 2.0) \times 10^12 cm^-2。 由于氟化学的简单性，CF+ 的柱密度与氟丰度成正比。 因此，我们推断气相氟的丰度为 F/H = (0.6 - 1.5) \times 10^-8。 光化学模型表明，CF+ 存在于 C+ 富集的层中。 发射来自被紫外线照射的星云皮肤，追踪最外层的云层。 事实上，CF+ 和 C+ 是迄今为止在马头星云中唯一被观测到的具有由动力学引起的双峰线轮廓的物种。 因此，我们认为可以从地面探测到的 CF+ 可以作为 C+ 层的替代指标。