Understanding Stellar Mass–Metallicity and Size Relations in Simulated Ultrafaint Dwarf Galaxies

Abstract

Reproducing the physical characteristics of ultrafaint dwarf galaxies (UFDs) in cosmological simulations is challenging, particularly with respect to stellar metallicity and galaxy size. To investigate these difficulties in detail, we conduct high-resolution simulations ( M gas ∼ 60 M ⊙ , M DM ∼ 300 M ⊙ ) on six UFD analogs ( M vir ∼ 10 8 –10 9 M ⊙ , M ⋆ ∼ 10 3 –2.1 × 10 4 M ⊙ at z = 0). Our findings reveal that the stellar properties of the UFD analogs are shaped by diverse star-forming environments from multiple progenitor halos in the early Universe. Notably, our UFD analogs exhibit a better match to the observed mass–metallicity relation, showing higher average metallicity compared to other theoretical models, though our results remain 0.5–1 dex lower than for observed UFDs. The metallicity distribution functions (MDFs) of our simulated UFDs lack high-metallicity stars ([Fe/H]≥ −2.0) while containing low-metallicity stars ([Fe/H]