New insights and predictions on high-redshift galaxies from wide-area infrared surveys

What do galaxies that formed right after the Big Bang look like? Are they as massive as the Milky Way is today? Do they already contain old stellar populations and galactic dust? In this PhD thesis, I used wide-area infrared galaxy surveys to investigate the presence and physical properties of galaxies billions of light years away. In Chapter 2, I simulated data for the newly-operating Euclid space telescope to assess its ability to identify early Universe galaxies, and how sample contamination from less distant galaxies with similar observational properties can be mitigated. In Chapter 3, I studied one particularly massive galaxy in the early Universe with various model fitting codes to quantify the effects of modelling assumptions on the stellar mass estimates. In Chapter 4, I studied a sample of infrared sources that are undetected at optical wavelengths with deep, high-resolution imaging from the James Webb Space Telescope to uncover their physical properties and study their Halpha emission. In Chapter 5, I placed the stellar properties of galaxies detected at sub-millimeter wavelengths in the context of comparable infrared galaxies that are undetected at such long wavelengths. In the final chapter, I summarize my findings on early Universe galaxies and discuss how synergies between existing and future infrared facilities will greatly increase statistics on these interesting sources.