High-z Lyman break galaxies with JWST: parallel observations of dwarf satellites

Dwarf galaxies are the most common type of galaxies in the Universe at all epochs and they play a fundamental role in cosmic history, being responsible for the build up of massive galaxies and possibly driving the reionization and metal enrichment processes. High-redshift observations of such sources are not available yet, but we demonstrate that the James Webb Space Telescope (JWST), while targeting massive Lyman Break Galaxies (LBGs), will catch for the first time the light of the faint satellite dwarf galaxies orbiting around them. We use state-of-art cosmological simulations of a typical LBG at z=6 to uncover the properties of satellite galaxies and make predictions for the upcoming JWST observations. These dwarf galaxies cover a wide range of stellar masses (log(M⋆/M⊙)≃7−9). We find that, even in such extremely dense environments, internal supernovae feedback is the key mechanism regulating their evolution, capable of completely quenching dwarf galaxies. Only the frequent merger events characterising these biased regions can effectively prolong the star-formation in the most massive satellites. Modelling the galaxies' stellar emission we reconstruct their spectral energy distributions: these reveal how with the JWST/NIRCam instrument, through colour-magnitude diagrams, it will be possible to infer properties such as the galaxies' stellar masses and ages. The instrument's high resolution will allow us to spatially resolve these small systems from the nearby host. Thanks to JWST's high sensitivities we will detect, for the very first time, faint satellite dwarf galaxies of high-z LBGs in less than 5 hours.