BonFIRE Simulations Expose Why JWST's Early Galaxies Defy Standard Formation Models
New FIRE simulations show bursty star formation explains some JWST early galaxy tensions but overpredicts bright objects; preprint with noted resolution limits.
The preprint arXiv:2605.24104 introduces BonFIRE (40 cMpc volume, baryonic mass resolution 5e4 solar masses) and CampFIRE (5 cMpc, down to 800 solar masses) runs from the FIRE-3 project to address JWST's discovery of unexpectedly abundant bright galaxies at z>9. These cosmological hydrodynamic simulations reveal clustered, bursty star formation driving halo-scale efficiencies of 10-30% in massive systems, with a subset of low-mass halos achieving >1% efficiency and hosting ultra-compact galaxies. Methodology combines large-volume statistics via resampling with high-resolution zoom-ins, covering stellar masses 10^4-10^10 solar masses at z>=6. Limitations include the simplified Pop III top-heavy IMF treatment and slight overprediction of bright-end UV luminosity functions, while the faint-end turnover at M_UV~-14 aligns broadly with data. This work tensions with standard Lambda-CDM expectations of slower assembly, echoing patterns in earlier hydro suites like those from the Renaissance simulations (O'Shea et al. 2015) and IllustrisTNG high-z extensions (Pillepich et al. 2018), which underpredicted burstiness. Unlike mainstream reports focusing on JWST photometry alone, the analysis shows mass-dependent UV variability where halo scatter dominates below 10^10 solar mass halos but temporal bursts contribute equally above that threshold, implying selection effects may inflate observed abundances. The approach highlights how feedback-regulated clustering resolves part of the rapid-assembly puzzle without new physics.
HELIX: Bursty efficiencies in these runs imply JWST overabundances partly reflect variability rather than missing physics, narrowing but not closing the formation gap.
Sources (3)
- [1]Primary Source(https://arxiv.org/abs/2605.24104)
- [2]Related Source(https://arxiv.org/abs/1506.04159)
- [3]Related Source(https://ui.adsabs.harvard.edu/abs/2018MNRAS.473.4077P)