First Light And Reionisation Epoch Simulations (FLARES) VI: The colour evolution of galaxies $z=5-15$

TL;DR

This paper predicts the colour evolution of high-redshift galaxies ($z=5-15$) using cosmological simulations, highlighting the impact of nebular emission and comparing results with existing observations and models.

Contribution

It introduces detailed predictions of galaxy colour evolution at high redshift from the FLARES simulations, emphasizing nebular line effects and model differences.

Findings

Predicted complex colour evolution driven by nebular lines.

Good agreement with existing Hubble, Spitzer, and early Webb data.

Key differences with other models in nebular emission strength.

Abstract

With its exquisite sensitivity, wavelength coverage, and spatial and spectral resolution, the James Webb Space Telescope is poised to revolutionise our view of the distant, high-redshift ($z>5$) Universe. While Webb's spectroscopic observations will be transformative for the field, photometric observations play a key role in identifying distant objects and providing more comprehensive samples than accessible to spectroscopy alone. In addition to identifying objects, photometric observations can also be used to infer physical properties and thus be used to constrain galaxy formation models. However, inferred physical properties from broadband photometric observations, particularly in the absence of spectroscopic redshifts, often have large uncertainties. With the development of new tools for forward modelling simulations it is now routinely possible to predict observational quantities, enabling a direct comparison with observations. With this in mind, in this work, we make predictions for the colour evolution of galaxies at $z=5-15$ using the FLARES: First Light And Reionisation Epoch Simulations cosmological hydrodynamical simulation suite. We predict a complex evolution, driven predominantly by strong nebular line emission passing through individual bands. These predictions are in good agreement with existing constraints from Hubble and Spitzer as well as some of the first results from Webb. We also contrast our predictions with other models in the literature: while the general trends are similar we find key differences, particularly in the strength of features associated with strong nebular line emission. This suggests photometric observations alone should provide useful discriminating power between different models.