Balmer breaks in simulated galaxies at z>6

TL;DR

This study examines whether current high-redshift galaxy simulations can reproduce the large Balmer breaks observed in some galaxies, finding they generally cannot, which suggests these galaxies may be rare or simulations incomplete.

Contribution

The paper evaluates the ability of existing simulations to replicate observed Balmer breaks in z>6 galaxies, highlighting potential gaps in current models.

Findings

Simulations struggle to produce large Balmer breaks seen in some high-z galaxies.

MACS1149-JD1 may be a rare object or simulations lack key physics.

Predictions for upcoming JWST observations are provided.

Abstract

Photometric observations of the spectroscopically confirmed $z\approx 9.1$ galaxy MACS1149-JD1 have indicated the presence of a prominent Balmer break in its spectral energy distribution, which may be interpreted as due to very large fluctuations in its past star formation activity. In this paper, we investigate to what extent contemporary simulations of high-redshift galaxies produce star formation rate variations sufficiently large to reproduce the observed Balmer break of MACS1149-JD1. We find that several independent galaxy simulations are unable to account for Balmer breaks of the inferred size, suggesting that MACS1149-JD1 either must be a very rare type of object or that our simulations are missing some key ingredient. We present predictions of spectroscopic Balmer break strength distributions for $z\approx 7-9$ galaxies that may be tested through observations with the upcoming James Webb Space Telescope and also discuss the impact that various assumptions on dust reddening, Lyman continuum leakage and deviations from a standard stellar initial mass function would have on the results.