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Speaker: Thịnh NguyễnDate/Time: March 7, 2025 / 12 noon central.Location: NCSA 1040Zoom: https://illinois.zoom.us/j/82318062756?pwd=M3g1MFF6cytsOWFEbmU0UW1XWVoxQT09Title: Effect of molecular hydrogen self-shielding modeling on galaxy formation in cosmological simulationAbstract: Accurately modeling molecular hydrogen H2 is an important task in cosmological simulations because it affects star formation and galaxy evolution. One fundamental property of molecular hydrogen is the ability to self-shield, a phenomenon in which the Lyman-Werner UV absorption line bands become optically thick at high H2 column density, and H2 in a molecular cloud's outer layer can shield H2 inside. Historically, numerical approximations have been utilized to avoid intensive ray-tracing calculations without significantly changing results. This paper evaluates the use of the Sobolev-like approximation in self-shielding modeling and tests whether it agrees with the results from a more rigorous ray tracing method in the cosmological simulation context. We run two sets of high-resolution zoom-in cosmological simulations, each set with two self-shielding models, to investigate the models' effects on galaxy evolution in the early stage and the late stage of the Reionization era. We find that the approximation model underestimates the level of H2 self-shielding in a low gas density environment, causing halos to lose a lot of H2 when compared with the ray tracing model. The susceptibility of H2 against high-energy radiation in simulations with the approximation model prevents smaller halos from forming stars, while bigger halos seem to be uninfluenced by the choice of self-shielding model in terms of stellar mass. Within a halo, we show that the discrepancy between the approximation and the ray-tracing model is more prominent in the halo's outer region due to its low gas density. On a large scale, the approximation model has fewer metal-contaminated regions in the intergalactic medium, increases IGM heating, and speeds up the reionization process. These results show that the use of Sobolev-like approximation to model H2 self-shielding alters various properties of galaxies and the large-scale universe, emphasizing a need for caution when employing this technique in running cosmological simulations.