Cumulative stellar mass during the first 2 Gyr. Each dashed line represents the stellar mass of each model galaxy simulated in a magnetic field model with strength varying from B_λ = 0.05 to 0.50 nG, compared with the model without magnetic field. Each solid line represents the mean stellar mass of all galaxies simulated in each model. The upper and lower panels correspond to all the models in ΛCDM and ΛCDM+PMFs settings, respectively. Top: Magnetic fields delay the formation of first stars. In low-mass halos of ultra-faint dwarf galaxies, B_λ = 0.50 nG completely prevents the star formation. In order to include halos which do not form any stars in the plot, their stellar masses are shown at 4 × 10³ M_⊙. Bottom: The influence of primordial magnetic fields on the matter power spectrum accelerates the formation of the first dark matter halos, leading to an earlier onset of star formation but an overall reduction in the final stellar mass.