Extensions to models of the galaxy-halo connection

We explore two widely used empirical models for the galaxy-halo connection, subhalo abundance matching (SHAM) and the halo occupation distribution (HOD), and compare them with the hydrodynamical simulation IllustrisTNG (TNG) for multiple statistics quantifying the galaxy distribution at n(gal) approximate to 1.3 x 10(-3) (Mpc h(-1))(-3). We observe that in their most straightforward implementations, both models fail to reproduce the two-point clustering measured in TNG. We find that SHAM models that use the relaxation velocity, V-relax, and the peak velocity, V-peak, perform best, and match the clustering reasonably well, although neither captures adequately the one-halo clustering. Splitting the total sample into sub-populations, we discover that SHAM overpredicts the clustering of high-mass, blue, star-forming, and late-forming galaxies and underpredicts that of low-mass, red, quiescent, and early-forming galaxies. We also study various baryonic effects, finding that subhaloes in the dark-matter-only simulation have consistently higher values of their SHAM-proxy properties than their full-physics counterparts. We then consider a 2D implementation of the HOD model augmented with a secondary parameter (environment, velocity anisotropy, sigma(2) Rhalf-mass, and total potential) tuned so as to match the two-point clustering of the IllustrisTNG galaxies on large scales. We analyse these galaxy populations adopting alternative statistical tools such as galaxy-galaxy lensing, void-galaxy cross-correlations, and cumulants of the density field, finding that the hydrodynamical galaxy distribution disfavours sigma(2) Rhalf-mass and the total potential as secondary parameters, while the environment and velocity anisotropy samples are consistent with full physics across all statistical probes examined. Our results demonstrate the power of examining multiple statistics for determining the secondary parameters that are vital for understanding the galaxy-halo connection.

Automated summary

The study explores the empirical models of subhalo abundance matching and halo occupation distribution for the galaxy-halo connection, comparing them with hydrodynamical simulation IllustrisTNG. Results indicate that both models, in their simplest forms, fail to accurately reproduce the clustering measured in the simulation. Further analysis reveals discrepancies in the predictions of high-mass, blue, star-forming galaxies compared to low-mass, red, quiescent galaxies.