Galaxy Formation Across Cosmic Time: From Halo Occupation to Galaxy Structure
Date:
Upcoming imaging surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will provide high-precision clustering measurements, requiring robust methods to connect galaxies with their dark matter haloes. In the first part of this talk, I will present a method to estimate halo occupation distributions directly from photometric data, adapted for LSST-like observations and tested using the CosmoDC2 mock galaxy catalog. In the second part, I will discuss the origin of extremely compact massive galaxies observed at high redshift by the James Webb Space Telescope. Using the high-resolution FirstLight simulations, we show that galaxies undergo a cycle of expansion, compaction, and re-expansion driven by gas inflows that trigger intense central star formation. This process can naturally produce the very small galaxy sizes observed at $z\gtrsim6$ and suggests the presence of a universal wet-compaction phase during cosmic dawn.