LEGO II：3 mm分子线研究，覆盖Milky Way圆盘内最活跃的恒星形成部分之一的100 pc
LEGO II: A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way Disc
摘要：
目前这一代的（亚）毫米望远镜已经使分子谱线发射成为研究河外星系的物理、运动学和化学性质的主要工具，但利用这些观测结果需要详细了解发射谱线在银河系内的起源。在本文中，我们提出了60 $^{\prime\prime}$（$\sim$ 3 pc）分辨率的观测，许多3毫米波段的分子线在一个大的地图W 49大质量恒星形成区（$\sim$ 100 $\times$ 100 pc在11千秒差距），这是采取的一部分，“乐高”IRAM-30米大项目。我们发现，分子谱线跃迁的空间范围或亮度与它们的临界密度没有很好的相关性，在估计谱线发射特性时，必须考虑突出丰度和光学深度。我们探讨如何总发射和发射效率（即每H $_{2}$柱密度的线亮度）的线发射作为分子氢柱密度和尘埃温度的函数而变化。我们发现，有没有一个单一的区域，这个参数空间负责最明亮，最有效地发射气体的所有物种。例如，我们发现HCN跃迁在高柱密度（$10^{22}$ cm $^{-2}$）和中等温度（35 K）下显示出高发射效率，而例如N $_2$ H $^+$朝向较低温度（$10^{22}$ cm $^{-2}$ ; <20 K）发射最有效。我们确定了$X_{\mathrm{CO} (1-0)} \sim 0.3 \times 10^{20} \mathrm{cm^{-2}(Kkms^{-1})^{-1}}$和$α_{\mathrm{HCN} (1-0)} \sim 30\mathrm{M_\odot(Kkms^{-1}pc^2)^{-1}}$，这两个值与通常采用的值有显著差异。总之，这些结果表明，在解释分子谱线发射时应谨慎。
英文摘要：
The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60$^{\prime\prime}$ ($\sim$3pc) resolution observations of many 3mm-band molecular lines across a large map of the W49 massive star-forming region ($\sim$100$\times$100pc at 11kpc), which were taken as part of the "LEGO" IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H$_{2}$ column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density ($10^{22}$cm$^{-2}$) and moderate temperatures (35K), whilst e.g. N$_2$H$^+$ emits most efficiently towards lower temperatures ($10^{22}$cm$^{-2}$; <20K). We determine $X_{\mathrm{CO} (1-0)} \sim 0.3 \times 10^{20} \mathrm{cm^{-2}(Kkms^{-1})^{-1}}$, and $α_{\mathrm{HCN} (1-0)} \sim 30\mathrm{M_\odot(Kkms^{-1}pc^2)^{-1}}$, which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.
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