Galaxy assembly bias and large-scale distribution: a comparison between
  IllustrisTNG and a semi-analytic model
  In this work, we compare large scale structure observables for stellar mass
selected samples at $z=0$, as predicted by two galaxy models, the
hydrodynamical simulation IllustrisTNG and the Santa-Cruz semi-analytic model
(SC-SAM). Although both models have been independently calibrated to match
observations, rather than each other, we find good agreement between the two
models for two-point clustering and galaxy assembly bias signatures. The models
also show a qualitatively similar response of occupancy and clustering to
secondary halo paramaters other than mass, such as formation history and
concentration, although with some quantitative differences. Thus, our results
demonstrate that the galaxy-halo relationships in SC-SAM and TNG are quite
similar to first order. However, we also find areas in which the models differ.
For example, we note a strong correlation between halo gas content and
environment in TNG, which is lacking in the SC-SAM, as well as differences in
the occupancy predictions for low-mass haloes. Moreover, we show that
higher-order statistics, such as cumulants of the density field, help to
accurately describe the galaxy distribution and discriminate between models
that show degenerate behavior for two-point statistics. Our results suggest
that SAMs are a promising cost-effective and intuitive method for generating
mock catalogues for next generation cosmological surveys.
