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Abstract

Dust obscures astronomical observations and plays a important role in the evolution of galaxies. Mapping dust in three dimensions not only allows accurate correction of observations but also constrains the evolution of the interstellar medium (ISM). Extinction is the central observable to trace the density and properties of dust, and is widely employed in dust mapping. Most existing dust maps assume a universal extinction curve, treating the properties of dust as uniform. This thesis introduces variations in the slope of extinction curves, parameterized by R(V). I construct a data-driven forward model that predicts low-resolution spectra as a function of stellar parameters (effective temperature, surface gravity, and metallicity), parallax, and extinction properties. This model is applied to all 220 million Gaia XP spectra, yielding precise extinction curves for 130 million stars in the Milky Way, LMC, and SMC. From these, I construct the first 3D all-sky map of extinction curve variations. Unexpectedly, I find extinction curves steepen, rather than flatten, with increasing dust density in translucent dust clouds. I propose a theoretical explanation, attributing the steepening to the growth of polycyclic aromatic hydrocarbons (PAHs). The results also provide implications for future observations in the era of the JWST.