Nature Astronomy (2019)
Future astronomical surveys will gather information that will allow gravity to be tested on cosmological scales, where general relativity is currently poorly constrained. We present a set of cosmological hydrodynamical simulations that follow galaxy formation in f(R) modified gravity models and are dedicated to finding observational signatures to help distinguish general relativity from alternatives using this information. The simulations employ the IllustrisTNG model and a new modified gravity solver in AREPO, allowing the interplay of baryonic feedback and modified gravity to be studied in the same simulation, and the degeneracy between them in the matter power spectrum to be resolved. We find that the neutral hydrogen power spectrum is suppressed substantially in f(R) gravity, which allows this model to be constrained using upcoming data from the Square Kilometre Array. Disk galaxies can form in our f(R) gravity simulations, even in the partially screened regime, and their galaxy stellar properties are only mildly affected. We conclude that modified gravity allows the formation of realistic galaxies and leaves observable signatures on large scales.