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 LCDM 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 LCDM, 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.
