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

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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.