Resolving the problem of galaxy clustering on small scales: any new
  physics needed?
  Galaxy clustering sets strong constraints on the physics governing galaxy
formation and evolution. However, most current models fail to reproduce the
clustering of low-mass galaxies on small scales ($r<1Mpc/h$). In this paper we
study the galaxy clusterings predicted from a few semi-analytical models. We
firstly compare two Munich versions, Guo et al. (2011, Guo11) and De Lucia \&
Blazoit (2007, DLB07). The Guo11 model well reproduces the galaxy stellar mass
function, but over-predicts the clustering of low-mass galaxies on small
scales. The DLB07 model provides a better fit to the clustering on small
scales, but over-predicts the stellar mass function. These seem to be puzzling.
We find that there is slightly more fraction of satellite galaxies residing in
massive haloes in the Guo11 model, which is the dominant contribution to the
clustering discrepancy between the two models. However, both models still
over-predict the clustering at $0.1Mpc/h<r<10Mpc/h$ for low mass galaxies. This
is because both models over-predict the number of satellites by $30\%$ in
massive halos than the data. Actually, the better agreement of DLB07 model with
the data on small scales comes as a coincidence as it predicts too many
low-mass central galaxies which are less clustered and thus bring down the
total clustering. Finally, we show the predictions from the semi-analytical of
Kang et al. (2012). We find that this model can simultaneously fit the stellar
mass function and galaxy clustering if the supernova feedback in satellite
galaxies is stronger. We conclude that semi-analytical models are now able to
solve the small-scales clustering problem, without invoking of any other new
physics or changing the dark matter properties, such as the recent favored warm
dark matter.
