Semi-analytic galaxy formation in f(R)-gravity cosmologies

Modifications of the equations of general relativity at large distances offer one possibility to explain the observed properties of our Universe without invoking a cosmological constant. Numerous proposals for such modified gravity cosmologies exist, but often their consequences for structure formation in the non-linear sector are not yet accurately known. In this work, we employ high-resolution numerical simulations of f (R)-gravity models coupled with a semi-analytic model (SAM) for galaxy formation to obtain detailed predictions for the evolution of galaxy properties. The f (R)-gravity models imply the existence of a 'fifth-force', which is however locally suppressed, preserving the successes of general relativity on Solar system scales. We show that dark matter haloes in f (R)-gravity models are characterized by a modified virial scaling with respect to the Lambda cold dark matter (Lambda CDM ) scenario, reflecting a higher dark matter velocity dispersion at a given mass. This effect is taken into account in the SAM by an appropriate modification of the mass-temperature relation. We find that the statistical properties predicted for galaxies (such as the stellar mass function and the cosmic star formation rate) in f (R)-gravity show generally only very small differences relative to Lambda CDM, smaller than the dispersion between the results of different SAM models, which can be viewed as a measure of their systematic uncertainty. We also demonstrate that galaxy bias is not able to disentangle between f (R)-gravity and the standard cosmological scenario. However, f (R)-gravity imprints modifications in the linear growth rate of cosmic structures at large scale, which can be recovered from the statistical properties of large galaxy samples.