FOREVER22: The first bright galaxies with population III stars at redshifts z ≈ 10-20 and comparisons with JWST data

Yajima, Hidenobu,   Abe, Makito,   Fukushima, Hajime,   Ono, Yoshiaki,   Harikane, Yuichi,   Ouchi, Masami,   Hashimoto, Takuya,   & Khochfar, Sadegh

Abstract

We study the formation of the first galaxies in overdense regions modelled by the FOREVER22 simulation project. Our simulations successfully reproduce the star formation rates and the M_UV - M_star relations of candidate galaxies at z ~ 10 - 14 observed by James Webb Space Telescope (JWST). We suggest that the observed galaxies are hosted by dark-matter haloes with M_h ≳ 10¹⁰ M_⊙andareinshort- periodstarburstphases.Ontheotherhand,evensimulatedmassivegalaxiesinoverdenseregionscannotreproducetheintensestarformationratesandthelargestellarmassesofobservedcandidatesatz~ 16. Also, we show that the contribution of population III stars to the UV flux decreases as the stellar mass increases and it is a few per cent for galaxies with M_star ~ 10⁷ M_⊙.Therefore,apartoftheobservedfluxbyJWSTcouldbethelightfrompopulationIIIstars.OursimulationssuggestthattheUVfluxcanbedominatedbypopulationIIIstarsandtheUV- slopeshowsβ ≲ -3 if future observations would reach galaxies with M_stars ~ 10⁵ M_⊙atz~ 20 of which the mass fraction of population III stars can be greater than 10 per cent.