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

Jordan C. J. D'Silva, Claudia D. P. Lagos, Luke J. M. Davies, Christopher C. Lovell, Aswin P. Vijayan

Published 2022-08-12Version 1

We use two independent, cosmological galaxy formation simulations, FLARES, a 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 (eg. 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 JWST to be able to observe every intrinsically bright galaxy up to ${z\sim10}$ (down to stellar masses of $\approx 10^{8.3}\,\rm M_{\odot}$ and SFRs of $\approx 1\,\rm M_{\odot}\, yr^{-1}$) in modest integration times. JWST will therefore be able to accurately constrain the parameters of the SFS given current proposed survey areas (e.g. the Webb COSMOS $0.7\,\rm deg^2$). 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 effect of chemical enrichment upon the observed light from galaxies (with FLARES predicting much less dust attenuation compared to SHARK that that we attribute to SHARK's quick metal enrichment). JWST observations will allow us to distinguish between these models, leading to a significant improvement upon our understanding of the formation of the very first galaxies.