Probing molecular line emission across the massive Galactic star forming region W49 in an extragalactic context

我们提出了一个为期三年的博士项目，这将为我们对银河系恒星形成和分子云的理解做出实质性的贡献。该项目嵌入在IRAM 30米望远镜大项目LEGO中，这是一项全面的500小时毫米波调查，提供了银河系中不同分子云样本的广泛光谱线测绘数据，并特别侧重于帮助解释最近一系列星系外调查的数据，这些调查只能以低得多的分辨率进行观测。随着新一代（亚）毫米望远镜（如ALMA和NOEMA）的出现，其他星系正成为这种专门调查的焦点，覆盖了越来越多样化的分子线，并推动了单个分子云的规模。因此，通过对银河系大质量恒星形成区域的分子线发射进行深入研究，这是连接这两个领域的理想时机。该项目将为该领域未来的许多观测设定基准。我们的团队已经发表了一项关于其中一个来源（W49）的试点研究，有了这些数据，再加上我们团队使用APEX望远镜进行的额外的新观测，这为一个高影响力的博士项目提供了一个绝好的机会，可以利用这个来源的丰富数据。该项目将分为以下三个不同的工作包（WP），这些工作包对博士生来说具有重大的科学潜力：WP-1)研究CO的激发（作为mm窗口内最常见的分子物种）作为W49中大块分子气体物理条件的示踪剂；WP-2)使用规范线比以及3mm和1mm窗口的全套线来研究它们作为环境函数的变化，这将限制它们作为局部（例如密度和温度变化）的经验探针的诊断能力；WP-3)在银河系和邻近的星系外系统内进行分子线发射诊断的第一次严格的定量比较。虽然这些工作包代表了项目的核心，但分析无疑会发现许多有趣的结果，为学生提供了充分的机会来进行后续观察和项目。

We propose a three-year PhD project that will provide a substantial contribution to our understanding of star formation and molecular clouds in the Milky Way. The project is embedded in the IRAM 30m telescope Large Program LEGO, a comprehensive 500h mm-wave survey providing extensive spectral line mapping data on a diverse sample of molecular clouds in the Milky Way and with a particular focus on helping to interpret data from a range of recent extragalactic surveys, which can only observe at much lower resolution. With the advent of the current generation of (sub)mm-telescopes such as ALMA and NOEMA, other galaxies are becoming the focus of such dedicated surveys, covering an increasingly diverse set of molecular lines and pushing to scales of individual molecular clouds. Hence, this is the ideal time to connect these two fields via the proposed in-depth study of molecular line emission across massive star-forming regions in the Milky Way. This project will set a benchmark for many future observations within the field. Our group has already published a pilot study on one of these sources (W49), and with these data, along with additional, new observations from our team with the APEX telescope, this represents a perfect opportunity for a high-impact PhD project exploiting the wealth of data on this source. The project will be broken down into the following three distinct work packages (WP) that have significant scientific potential for the PhD student: WP-1) studying the excitation of CO (as the most commonly observed molecular species within the mm-window) as a tracer of the physical conditions of the bulk molecular gas across W49; WP-2) using canonical line ratios as well as the full suite of lines across the 3mm and 1mm window to study their variation as a function of environment, which will place constraints on their diagnostic power as empirical probes of local e.g. density and temperature variations; WP-3) Conduct the first rigorous quantitative comparison of molecular line emission diagnostics within the Milky Way and nearby extragalactic systems. While these work packages represent the core of the project, the analysis will undoubtedly uncover many interesting results providing ample opportunity for the student to pursue follow-up observations and projects.