A flexible modelling of galaxy assembly bias
  We use the {\sc Illustris TNG300} magneto-hydrodynamic simulation, the {\sc
SAGE} semi-analytical model, and the subhalo abundance matching technique
(SHAM) to examine the diversity in predictions for galaxy assembly bias (i.e.
the difference in the large scale clustering of galaxies at a fixed halo mass
due to correlations with the assembly history and other properties of host
haloes). We consider samples of galaxies selected according to their stellar
mass or star formation rate at various redshifts. We find that all models
predict an assembly bias signal of different magnitude, redshift evolution, and
dependence with selection criteria and number density. To model these
non-trivial dependences, we propose an extension to the standard SHAM technique
so it can include arbitrary amounts of assembly bias. We do this by
preferentially selecting subhaloes with the same internal property but
different {\it individual} large-scale bias. We find that with this model, we
can successfully reproduce the galaxy assembly bias signal in either {\sc SAGE}
or the {\sc TNG}, for all redshifts and galaxy number densities. We anticipate
that this model can be used to constrain the level of assembly bias in
observations and aid in the creation of more realistic mock galaxy catalogues.
