JWST Imaging of 74 Nearby Galaxies, and Establishing PAH Emission as a Sensitive, High-resolution Tracer of Cold Gas
Molecular gas is a cornerstone of the star formation cycle in galaxies, yet mapping its distribution and properties remains a significant challenge. In this talk, I will present new JWST observations of 55 nearby galaxies obtained as part of the PHANGS-JWST survey, bringing the total coverage to 74 galaxies. I will show new results leveraging the unparalleled sensitivity and resolution of these new JWST data to trace cold gas through infrared emission from polycyclic aromatic hydrocarbons (PAHs). This approach offers a powerful alternative to traditional tracers like CO, particularly in terms of sensitivity and resolution, and possibly even in regions where CO cannot be used as a gas tracer.
I will highlight two key outcomes of this research: First, I will showcase results from Chown et al. (2025), where we demonstrate a strong correlation between JWST PAH emission and ALMA CO(2-1) observations at ~100 pc resolution across 70 nearby star-forming galaxies from the PHANGS sample. This work establishes PAH emission as a robust tracer of cold gas, revealing filaments, shells and other structures in this gas with sharper resolution and better sensitivity than ALMA. PAH emission also traces HI gas, opening exciting new avenues for studying the interstellar medium. Second, I will present ongoing efforts to measure how regional variations in the radiation field, dust to gas ratio, and PAH abundance modulate the PAH-vs-gas relation.
This work not only advances our understanding of the cold gas content in galaxies but also paves the way for future JWST observations to map the gas in the universe with unprecedented detail. I will conclude by discussing the broader implications of this approach for studies of star formation, feedback, and galaxy evolution.
