Princeton University SFIR: Star Formation/ISM Rendezvous

I will present the first three-dimensional, full-sky dust map with variations in extinction curves, parameterized by R(V). Leveraging Gaia XP spectra, we have determined extinction curves for 130 million stars—two order of magnitude more than previously available—enabling us to trace the dust properties of the Milky Way and the Magellanic Clouds with unprecedented precision. Surprisingly, we find that R(V) decreases, rather than increases, with dust column density in the translucent regions of multiple clouds. Both theoretical arguments and observational evidence suggest that this trend is driven by the growth of polycyclic aromatic hydrocarbons (PAHs). These results not only identify promising regions of PAH formation for follow-up observations, but also reveal a potentially rapid, in-situ pathway to account for the PAH absorption seen in galaxies at cosmic dawn (z~7). Future multi-wavelength follow-up observations of strongly lensed galaxies can offer a unique opportunity to probe the physical and chemical environments that shape dust formation and trace the chemical evolution of galaxies.