Towards a consistent framework of comparing galaxy mergers in
  observations and simulations
  Aims. We aim to perform consistent comparisons between observations and
simulations on the mass dependence of the galaxy major merger fraction at low
redshift over an unprecedentedly wide range of stellar masses (10^9 to 10^12
solar masses).
  Methods. We first carry out forward modelling of ideal synthetic images of
major mergers and non-mergers selected from the Next Generation Illustris
Simulations (IllustrisTNG) to include major observational effects. We then
train deep convolutional neural networks (CNNs) using realistic mock
observations of galaxy samples from the simulations. Subsequently, we apply the
trained CNNs to real the Kilo-Degree Survey (KiDS) images of galaxies selected
from the Galaxy And Mass Assembly (GAMA) survey. Based on the major merger
samples, which are detected in a consistent manner in the observations and
simulations, we determine the dependence of major merger fraction on stellar
mass at z around 0.15 and make comparisons between the two.
  Results. The detected major merger fraction in the GAMA/KiDS observations has
a fairly mild decreasing trend with increasing stellar mass over the mass range
10^9 < M_sun < M_star < 10^11.5 M_sun. There is good agreement in the mass
dependence of the major merger fraction in the GAMA/KiDS observations and the
IllustrisTNG simulations over 10^9.5 M_sun < M_star < 10^10.5 M_sun. However,
the observations and the simulations show some differences at M_star >
10^10.5M_sun, possibly due to the supermassive blackhole feedback in its
low-accretion state in the simulations which causes a sharp transition in the
quenched fractions at this mass scale. The discrepancy could also be due to the
relatively small volume of the simulations and/or differences in how stellar
masses are measured in simulations and observations.
