Unveiling the main sequence of galaxies at $z \geq 5$ with the James Webb Space Telescope: predictions from simulations

TL;DR

This study predicts that JWST will effectively observe and characterize the star-forming main sequence of galaxies at redshifts 5 to 10, using simulations to assess observational capabilities and model differences.

Contribution

It compares two independent galaxy formation simulations to forecast JWST's ability to measure galaxy properties and distinguish between different galaxy formation models at high redshift.

Findings

JWST can observe over 70-90% of galaxies up to z~10 in current survey areas.

Both simulations predict similar distributions but differ in galaxy abundance and quenching onset.

Observations will help differentiate galaxy formation models and improve understanding of early galaxy evolution.

Abstract

We use two independent, galaxy formation simulations, FLARES, a cosmological hydrodynamical simulation, and SHARK, a semi-analytic model, to explore how well the James Webb Space Telescope (JWST) will be able to uncover the existence and parameters of the star-forming main sequence (SFS) at $z=5\to10$, i.e. shape, scatter, normalisation. Using two independent simulations allows us to isolate predictions (e.g., stellar mass, star formation rate, SFR, luminosity functions) that are robust to or highly dependent on the implementation of the physics of galaxy formation. Both simulations predict that JWST can observe $\ge 70-90\%$ (for SHARK and FLARES respectively) of galaxies up to $z\sim10$ (down to stellar masses of $\approx 10^{8.3}\,\rm M_{\odot}$ and SFRs of $\approx 10^{0.5}\,\rm M_{\odot}\, yr^{-1}$) in modest integration times and given current proposed survey areas (e.g. the Web COSMOS $0.6\,\rm deg^2$) to accurately constrain the parameters of the SFS. Although both simulations predict qualitatively similar distributions of stellar mass and SFR, there are important quantitative differences, such as the abundance of massive, star-forming galaxies, with FLARES predicting a higher abundance than SHARK; the early onset of quenching as a result of black hole growth in FLARES (at $z\approx 8$), not seen in SHARK until much lower redshifts; and the implementation of synthetic photometry, with FLARES predicting more JWST-detected galaxies ($\sim 90\%$) than SHARK ($\sim 70\%$) at $z=10$. JWST observations will distinguish between these models, leading to a significant improvement upon our understanding of the formation of the very first galaxies.