Cake Talk by Kevin Harrington

The peak epoch of cosmic star formation also coincides with the peak in the cosmic co-moving molecular gas mass density, at z ~2. Even with sensitive interferometers, only strongly lensed galaxies offer the feasibility to efficiently and systematically detect multiple emission lines tracing the full CO ladder and both atomic carbon fine-structure lines for high-z galaxies. In the past few years, our team has delved into the Planck All-Sky Survey to Analyze Gravitationally-lensed Extreme Starbursts (PASSAGES) in order to conduct such systematic studies to better understand the most active star-forming galaxies in the early Universe. In this talk I will present the results of a state-of-the-art approach to model — simultaneously — both the detected emission lines and the dust SED. Using the largest assembly of ~200 CO/[CI] lines for any uniformly selected high-z sample, we have explicitly derived the infamous alpha conversion factors without assuming any excitation corrections or typically applied values. I will discuss the implications based on such spatially unresolved measurements, including a detailed perspective on the often-used dust continuum approach to deriving the molecular gas masses. I will also present our current understanding of the [CI] line excitation conditions in the context of these detailed radiative transfer models.

More details can be found in the recently published Harrington et al. 2021 (https://ui.adsabs.harvard.edu/abs/2021ApJ…908…95H/abstract    — the ApJ version is recommended; please see the supp tables/figs).