Exploring the Dark Age: Star and Galaxy formation in the Early Universe

Abstract: The Cosmic Dark Ages mark a pivotal era of the universe's evolution, transitioning from a neutral, opaque medium to the emergence of the first stars and galaxies that initiated cosmic reionization. This study examines the thermodynamics of the intergalactic medium (IGM), molecular hydrogen cooling, and gravitational collapse that led to structure formation. Key emission lines, such as Lyman-alpha (Ly$\alpha $) and [C II] 158 $\mu m$, are analyzed as tracers of star formation, metallicity, and IGM conditions. Simulations highlight Ly$\alpha $ scattering profiles and [C II] emission as critical diagnostics of early galaxy evolution. The findings provide a theoretical framework to interpret high-redshift observations, advancing our understanding of the universe's transition from darkness to illumination.