The Role of Halo Assembly History in Galaxy Evolution

Abstract

In the Lambda Cold Dark Matter (ΛCDM) paradigm, dark matter halos serve as the fundamental framework for galaxy formation. Recent studies show that, beyond halo mass, halo assembly history (how and when a halo grows) is a key factor in shaping galaxy properties. This review synthesizes theoretical insights and observational evidence on how assembly time and growth mode influence gas cooling, star formation, feedback, and morphology. Earlyforming halos often foster rapid starbursts and spheroidal structures, while late-forming halos sustain prolonged star formation and disk-like morphologies. The role of largescale environment and cosmic web connectivity further modulates these outcomes, contributing to observable trends such as color bimodality and galaxy clustering. Through comparisons of simulations, semi-analytic models, and observational probes, this paper demonstrates that halo assembly history is a critical secondary parameter in galaxy evolution, beyond mass alone. The implications for feedback processes, halo occupation models, and upcoming surveys are also discussed, emphasizing the need to incorporate assembly bias into future theoretical and empirical frameworks.