Comparing Galaxy Clustering in Horizon-AGN Simulated Lightcone Mocks and VIDEO Observations

TL;DR

This study compares galaxy clustering in Horizon-AGN simulations with VIDEO observations, highlighting discrepancies at low stellar masses and validating HOD modeling as a tool for understanding galaxy-halo relationships.

Contribution

It provides a detailed comparison of simulated and observed galaxy clustering, analyzing biases from SED-fitting and validating HOD modeling for galaxy-halo connection studies.

Findings

Horizon-AGN underestimates clustering at low stellar masses by up to a factor of 3.

Clustering and HOD results are qualitatively similar between simulation and observations.

HOD modeling effectively probes the galaxy-halo connection, validated by comparison with direct simulation measurements.

Abstract

Hydrodynamical cosmological simulations have recently made great advances in reproducing galaxy mass assembly over cosmic time - as often quantified from the comparison of their predicted stellar mass functions to observed stellar mass functions from data. In this paper we compare the clustering of galaxies from the hydrodynamical cosmological simulated lightcone Horizon-AGN, to clustering measurements from the VIDEO survey observations. Using mocks built from a VIDEO-like photometry, we first explore the bias introduced into clustering measurements by using stellar masses and redshifts derived from SED-fitting, rather than the intrinsic values. The propagation of redshift and mass statistical and systematic uncertainties in the clustering measurements causes us to underestimate the clustering amplitude. We find then that clustering and halo occupation distribution (HOD) modelling results are qualitatively similar in Horizon-AGN and VIDEO. However at low stellar masses Horizon-AGN underestimates the observed clustering by up to a factor of ~3, reflecting the known excess stellar mass to halo mass ratio for Horizon-AGN low mass haloes, already discussed in previous works. This reinforces the need for stronger regulation of star formation in low mass haloes in the simulation. Finally, the comparison of the stellar mass to halo mass ratio in the simulated catalogue, inferred from angular clustering, to that directly measured from the simulation, validates HOD modelling of clustering as a probe of the galaxy-halo connection.