Santa Cruz SAM Reveals Ultra-Short Assembly Timescales for z>12 Galaxies in GUREFT Merger Trees
Santa Cruz SAM applied to GUREFT trees shows rapidly rising yet bursty star-formation histories from Cosmic Dawn to z~6, with t50 and t90 timescales shortening sharply at higher redshift. Results imply that young stellar populations dominate ultra-high-z photometry and set the ionizing budget during reionization. The work bridges simulation and JWST data by providing observationally testable SFH distributions across the entire EoR.
The study couples halo merger trees from the GUREFT dark-matter-only suite with the Santa Cruz semi-analytic model to evolve galaxies from z~14 through the Epoch of Reionization. Median star-formation histories rise steeply and smoothly across all masses, yet individual tracks display stochastic bursts and brief quenching episodes that match the diversity now inferred from JWST spectroscopy. These patterns emerge because the model tracks gas cooling, feedback, and mergers self-consistently across cosmic time rather than assuming constant star-formation efficiency. The resulting stellar populations at the highest redshifts are overwhelmingly young, forcing revisions in how synthetic photometry is generated for Lyman-break selections. This framework directly links the compact, high-specific-star-formation-rate sources seen by JWST to the full timeline of reionization by predicting when and how much ionizing radiation each halo contributes. The main limitation remains the absence of resolved interstellar-medium physics, which future hydrodynamical zoom simulations calibrated to the same SAM can test.
JWST: Cycle 3 deep fields will show 75% of z>12 galaxies with mass-weighted ages below 40 Myr within the next 18 months.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2607.02650)
- [2]Supporting Source(https://ui.adsabs.harvard.edu/abs/2023ApJ...945...18Y)