Unveiling Galaxy Bias via the Halo Model, KiDS and GAMA
  We measure the projected galaxy clustering and galaxy-galaxy lensing signals
using the Galaxy And Mass Assembly (GAMA) survey and Kilo-Degree Survey (KiDS)
to study galaxy bias. We use the concept of non-linear and stochastic galaxy
biasing in the framework of halo occupation statistics to constrain the
parameters of the halo occupation statistics and to unveil the origin of galaxy
biasing. The bias function $\Gamma_{\text{gm}}(r_{\text{p}})$, where
$r_{\text{p}}$ is the projected comoving separation, is evaluated using the
analytical halo model from which the scale dependence of
$\Gamma_{\text{gm}}(r_{\text{p}})$, and the origin of the non-linearity and
stochasticity in halo occupation models can be inferred. Our observations
unveil the physical reason for the non-linearity and stochasticity, further
explored using hydrodynamical simulations, with the stochasticity mostly
originating from the non-Poissonian behaviour of satellite galaxies in the dark
matter haloes and their spatial distribution, which does not follow the spatial
distribution of dark matter in the halo. The observed non-linearity is mostly
due to the presence of the central galaxies, as was noted from previous
theoretical work on the same topic. We also see that overall, more massive
galaxies reveal a stronger scale dependence, and out to a larger radius. Our
results show that a wealth of information about galaxy bias is hidden in halo
occupation models. These models should therefore be used to determine the
influence of galaxy bias in cosmological studies.
