Limitations to the `basic' HOD model and beyond
Abstract
We use the IllustrisTNG cosmological, hydrodynamical simulations to test fundamental assumptions of the massbased halo occupation distribution (HOD) approach to modelling the galaxyhalo connection. By comparing the clustering of galaxies measured in the 300 Mpc TNG box (TNG300) with that predicted by the standard (basic) HOD model, we find that, on average, the 'basic' HOD model underpredicts the realspace correlation function in the TNG300 box by ∼15 per cent on scales of $1 \,\,\lt\,\, r \,\,\lt\,\, 20 \ {\rm Mpc}\, h^{1}$ , which is well beyond the target precision demanded of nextgeneration galaxy redshift surveys. We perform several tests to establish the robustness of our findings to systematic effects, including the effect of finite box size and the choice of halo finder. In our exploration of 'secondary' parameters with which to augment the 'basic' HOD, we find that the local environment of the halo, the velocity dispersion anisotropy, β, and the product of the halfmass radius and the velocity dispersion, σ^{2}R_{halfmass}, are the three most effective measures of assembly bias that help reconcile the 'basic' HODpredicted clustering with that in TNG300. In addition, we test other halo properties such as halo spin, formation epoch, and halo concentration. We also find that at fixed halo mass, galaxies in one type of environment cluster differently from galaxies in another. We demonstrate that a more complete model of the galaxyhalo connection can be constructed if we combine both mass and local environment information about the halo.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2020
 DOI:
 10.1093/mnras/staa623
 arXiv:
 arXiv:1911.02610
 Bibcode:
 2020MNRAS.493.5506H
 Keywords:

 methods: numerical;
 galaxies: haloes;
 largescale structure of Universe;
 cosmology: theory;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 15 pages, 10 figures, 2 tables