We explore the nature of the first galaxies using a semi-analytic model tailored for the rapidly evolving early Universe (Ventura et al. 2024). Applying this model to an N-body simulation enables us to resolve molecularly cooled minihalos down to ~1e5Msol within a cosmological volume of 10/h cMpc. By tracking chemical enrichment both inside and outside these first galaxies, we closely follow their stellar components and investigate the impact of Population III (Pop. III) stars on the early intergalactic medium (IGM). With this model we explored the sensitivity of the star formation rate density (SFRD) and stellar mass function (SMF) on the unknown free parameters.
In this presentation, I will demonstrate that the majority of the first galaxies are likely enriched by their own star formation with the metallicity of the IGM at z>=6 remaining below the critical value necessary to quench Pop. III star formation. However, as reionization progresses, the effects of photo-heating and photo-dissociating feedback from the UV background become more pronounced. This leads to a halt in star formation and subsequent metal production within these galaxies, with external chemical enrichment becoming more relevant (at z = 6 about 1% of the IGM volume is filled with metals).
By integrating this novel semi-analytic model with Pop. III stellar population synthesis, we predict the UV spectra and light-curve of the first galaxies, exploring how the abundance and properties of Pop III stars influence their detectability. I will discuss the intriguing prospect that the bright galaxies recently observed by JWST at z > 12 could be predominantly composed of Pop. III stars and characterized by a top-heavy initial mass function without requiring an increased star formation efficiency.
Antonino Milone
