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 Illustris'ING 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 parameters other than mass, such as formation history and concentration, although p 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 'MG, 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 us to accurately describe the galaxy distribution and discriminate between models that show degenerate behaviour 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.

Automated summary

In this study, two galaxy models (Illustris'ING and SC-SAM) were compared for their predictions on large scale structure observables for stellar mass selected samples at z=0. The models show good agreement in two-point clustering and galaxy assembly bias, but differences in areas such as halo gas content correlation with environment and occupancy predictions for low-mass haloes. Higher order statistics help accurately describe the galaxy distribution and differentiate between models showing similar behavior in two-point statistics. SAMs are suggested as a promising method for generating mock catalogues for future cosmological surveys.