Dwarf Satellites of High-z Lyman Break Galaxies: A Free Lunch for JWST

We show that the James Webb Space Telescope (JWST) will be able to detect dwarf satellites of high-z Lyman break galaxies (LBGs). To this end, we use cosmological simulations following the evolution of a typical M⋆ ≃ 1010 M⊙ LBG up to z ≃ 6, and analyze the observational properties of its five satellite dwarf galaxies (107 M⊙ < M⋆ < 109 M⊙). Modeling their stellar emission and dust attenuation, we reconstruct their rest-frame ultraviolet-optical spectra for 6 < z < 6.5. JWST/NIRCam synthetic images show that the satellites can be spatially resolved from their host, and their emission is detectable by planned deep surveys. Moreover, we build synthetic spectral energy distributions and color–magnitude diagrams for the satellites. We conclude that the color F200W–F356W is a powerful diagnostic tool for understanding their physical properties once they have been identified. For example, F200W–F356W ≲ −0.25 can be used to identify star-bursting (SFR ∼ 5 M⊙ yr−1), low-mass (M⋆ ≲ 5 × 108 M⊙) systems, with ∼80% of their stars being young and metal poor $[\mathrm{log}({Z}_{\star }/{Z}_{\odot })\lt -0.5$].