Realistic simulations of galaxy formation in f(R) modified gravity

We have carried out a set of cosmological hydrodynamical simulations that follow galaxy formation in $f(R)$ modified gravity models. Our simulations employ the Illustris-TNG full physics model and a new modified gravity solver in the AREPO code. For the first time we are able to investigate the degeneracy in the matter power spectrum between the effects of $f(R)$-gravity and feedback from active galactic nuclei (AGN), and the imprint of modified gravity on the properties of galaxies and on the distribution of dark matter, gas and stars in the universe. $f(R)$-gravity has an observable effect on the neutral hydrogen power spectrum at high redshift at a level of 20%. For both the F6 and F5 models, this is significantly larger than the predicted errors for the SKA1-MID survey, making this probe a powerful test of gravity on large scales. A similar effect is present in the power spectrum of the stars at high redshift. We also show that rotationally supported disc galaxies can form in $f(R)$-gravity, even in the partially screened regime. Our simulations indicate that there might be more disc galaxies in F6 compared to GR, and fewer in F5. Finally, we show that the back reaction between AGN feedback and modified gravity in the matter power spectrum is not important in the F6 model but has a sizeable effect in F5.