First Light And Reionisation Epoch Simulations (FLARES) V: The redshift frontier

TL;DR

This paper uses hydrodynamical simulations to predict properties of galaxies at redshifts greater than 10, aiding JWST observations and providing insights into early universe galaxy populations.

Contribution

First hydrodynamical model predictions for $z>10$ galaxies, validated at low redshift, to guide JWST observations of the early universe.

Findings

Predicted ~600 galaxies at $z>10$ in JWST's first cycle.

Broad agreement with current UV luminosity and slope constraints at $z=10$.

Tension with some recent $z\,\sim 13$ observational constraints.

Abstract

The James Webb Space Telescope (JWST) is set to transform many areas of astronomy, one of the most exciting is the expansion of the redshift frontier to $z>10$. In its first year alone JWST should discover hundreds of galaxies, dwarfing the handful currently known. To prepare for these powerful observational constraints, we use the First Light And Reionisation Epoch (FLARES) simulations to predict the physical and observational properties of the $z>10$ population of galaxies accessible to JWST. This is the first time such predictions have been made using a hydrodynamical model validated at low redshift. Our predictions at $z=10$ are broadly in agreement with current observational constraints on the far-UV luminosity function and UV continuum slope $\beta$, though the observational uncertainties are large. We note tension with recent constraints $z\sim 13$ from Harikane et al. 2022 - compared to these constraints, FLARES predicts objects with the same space density should have an order of magnitude lower luminosity, though this is mitigated slightly if dust attenuation is negligible in these systems. Our predictions suggest that in JWST's first cycle alone, around $600$ galaxies should be identified at $z>10$, with the first small samples available at $z>13$.