FOREVER22: the first bright galaxies with population III stars at redshifts $z \simeq 10-20$ and comparisons with JWST data

TL;DR

This paper models the formation of the first galaxies with Population III stars at very high redshifts, comparing simulations with JWST observations, and explores the contribution of Population III stars to early galaxy UV flux.

Contribution

It presents the first simulation-based analysis of Population III stars' role in early galaxy formation at redshifts 10-20, aligned with JWST data.

Findings

Simulations reproduce observed star formation rates at z~10-14.

Population III stars contribute a few percent to UV flux in early galaxies.

UV flux dominated by Population III stars if galaxies with M_star ~ 10^5 M_sun are observed at z~20.

Abstract

We study the formation of the first galaxies in overdense regions modelled by the FORmation and EVolution of galaxies in Extremely overdense Regions motivated by SSA22 (FOREVER22) simulation project. Our simulations successfully reproduce the star formation rates and the $M_{\rm UV}-M_{\rm star}$ relations of candidate galaxies at $z \sim 10-14$ observed by the James Webb Space Telescope (JWST). We suggest that the observed galaxies are hosted by dark-matter haloes with $M_{\rm h} \gtrsim 10^{10}~{\rm M_{\odot}}$ and are in short-period starburst phases. On the other hand, even simulated massive galaxies in overdense regions cannot reproduce the intense star formation rates and the large stellar masses of observed candidates at $z \sim 16$. 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 percent for galaxies with $M_{\rm star} \sim 10^{7}~{\rm M_{\odot}}$. Therefore, a part of the observed flux by JWST could be the light from population III stars. Our simulations suggest that the UV flux can be dominated by population III stars and the UV-slope shows $\beta \lesssim -3$ if future observations would reach galaxies with $M_{\rm stars} \sim 10^{5}~{\rm M_{\odot}}$ at $z \sim 20$ of which the mass fraction of population III stars can be greater than 10 percent.