"Modeling the CO SLEDs of High-Redshift Quasars: Constraining AGN Feedback and Molecular Gas Masses"

Abstract:

Luminous high-redshift quasars provide a unique laboratory to investigate the coevolution of supermassive black holes and their host galaxies during the early stages of galaxy assembly. In these systems, AGN feedback is expected to significantly affect the physical and chemical state of the interstellar medium (ISM), potentially regulating the cold molecular gas reservoir that fuels both star formation and SMBH accretion. Interpreting the observed molecular gas properties, therefore requires physically motivated models capable of linking the cold gas excitation to the underlying gas heating mechanisms.

In this talk, I will present a novel analysis of the CO spectral line energy distributions (CO SLEDs) of luminous high-redshift quasars based on a recent model that combines the internal density structure of giant molecular clouds with stellar heating in photon-dominated regions (PDRs) and AGN-driven heating in X-ray dominated regions (XDRs). Applying this methodology to quasars observed in multiple CO transitions allows us to quantify the contribution of AGN radiative feedback to the high-J CO excitation, while simultaneously deriving robust constraints on the CO-to-H2 conversion factor. For the best-sampled CO SLEDs, the inferred molecular gas masses can be constrained with uncertainties below 15%. These results demonstrate the importance of physically motivated CO SLED modeling to accurately constrain the molecular gas content and feedback processes in massive galaxies in the early Universe.