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Metallicity is one of the most powerful diagnostics of galaxy formation and evolution, encoding the cumulative history of gas accretion, star formation, feedback, and assembly. In this talk, I will begin with two basic mass-continuity equations governing gas and metal evolution in galaxies, showing how their analytic behaviour naturally explains a wide range of observed scaling relations. I will then present three case studies illustrating the breadth of insight metallicity offers. First, using the new COLIBRE simulation suite, I will demonstrate that metallicity provides a clean probe of the galaxy–halo connection and reveals that the concentration dependence of the stellar-to-halo mass relation arises from differences in gravitational potential depth. Second, I will revisit the widely discussed metallicity–size relation, showing that its physical driver is star-formation efficiency—rather than gravitational potential—with galaxy size acting as an indirect tracer of this efficiency. Third, I will show how these two continuity equations explains both the redshift evolution of the mass–metallicity relation and the form of the Fundamental Metallicity Relation (FMR), while predicting an even more fundamental scaling that depends only on the stellar initial mass function, offering a potential IMF diagnostic. Finally, I will introduce GALFORM++, the next-generation semi-analytical framework I am leading the development to enable highly flexible, modular experimentation across all aspects of galaxy formation physics.

BIO

Dr. Kai Wang is a Postdoctoral Research Associate at the Institute for Computational Cosmology and Centre for Extragalactic Astrophysics of Durham University. He received his BS (2017) from the University of Science and Technology of China and PhD (2022) from Tsinghua University. Prior to joining Durham, he was a KIAA Postdoctoral Fellow at the Kavli Institute for Astronomy and Astrophysics of Peking University (2022-2024). Dr. Wang's research focuses on galaxy formation and evolution within dark matter halos in a cosmological context, combining theoretical modeling with multi-wavelength observations. His work bridges semi-analytic approaches, hydrodynamic simulations, and observational datasets to understand how galaxies form and evolve within the cosmic web.