Galaxy assembly bias and large-scale distribution: a comparison between IllustrisTNG and a semi-analytic model

Abstract

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.

Galaxy Formation in the Santa Cruz semi-analytic model compared with IllustrisTNG -- I. Galaxy scaling relations, dispersions, and residuals at z=0

“…This same qualitative correlation between SMHM residual and halo concentration has been demonstrated in the EAGLE hydrodynamic simulations (Matthee et al 2017). This may also help explain why the assembly bias signal is so similar in the SC SAM and TNG, as halo concentration (or assembly history) is known to be one of the most important secondary halo parameters that influences clustering (Hadzhiyska et al 2021). In order to gain further insights into this question, in a follow-up paper we plan on investigating the stellar mass assembly histories as a function of time in TNG and the SC SAM (Gabrielpillai et al in prep.…”

“…We compared the halo mass functions from at various redshifts with those from applied to both the dark matter only and full physics run of TNG. We find very small differences between the dark matter only (DMO) results from and , consistent with the results presented by Gómez et al (2021) and Hadzhiyska et al (2021). As a supplementary verification step, we plotted the positions of the most massive halos in the and DMO catalogs along with overlaid circles of radius 𝑟 vir .…”

“…There is very good agreement, with no significant systematic offset, and a scatter of less than ±0.05 dex. The 3D position and velocity matches also show excellent agreement (see also Hadzhiyska et al 2021, who show the clustering properties of halos in these two sets of catalogs). For the comparison between -DMO and -FP (bottom panel), we see a more substantial offset with a trend with halo mass.…”

“…They found that TNG produced better agreement with these observables, but they were able to modify the -SAM to improve the agreement with observations and with TNG. Hadzhiyska et al (2021) compared predictions of galaxy clustering and assembly bias in the SC SAM and TNG, finding encouraging levels of agreement between both statistics. Furthermore, they studied the correlation of secondary halo properties, such as halo concentration and environment, on assembly bias.…”

“…When SAMs are run within halos extracted from N-body simulations, they can be used to make predictions for galaxy clustering (e.g. Kauffmann et al 1999;Somerville et al 2001;Hadzhiyska et al 2021).…”