What can galaxy clustering really tell us about the galaxy-halo connections?

TL;DR

This paper introduces CS-SHAM, a new galaxy-halo connection model that independently matches central and satellite galaxies, improving clustering predictions and revealing that clustering constrains galaxy occupation mainly in massive halos.

Contribution

The paper presents CS-SHAM, a novel framework with adjustable satellite fraction parameters, and demonstrates its effectiveness in reproducing galaxy clustering across different subhalo mass proxies.

Findings

CS-SHAM reliably reproduces galaxy clustering with different subhalo mass proxies.

Galaxy clustering constrains the halo occupation distribution mainly for massive halos.

Models cannot robustly constrain satellite fraction when using different mass proxies.

Abstract

Subhalo abundance matching (SHAM) is a commonly used framework for modeling the galaxy-halo connection. Yet, its standard implementation has difficulty reproducing the observed galaxy clustering with high accuracy (e.g., $\chi^2/\mathrm{dof} \approx 1$). To overcome this issue, we propose a novel CS-SHAM framework, in which central and satellite galaxies are independently matched to main and satellite subhalos in simulations. Within this scheme, we introduce three free parameters to explicitly characterize the satellite fraction, $f_{\mathrm{sat}}$, as a function of stellar mass or absolute magnitude. To evaluate the performance of CS-SHAM, we apply it to two sets of mock galaxy catalogs built with the conventional SHAM method but using different subhalo mass proxies, $M_{\mathrm{peak}}$ and $V_{\mathrm{peak}}$, as well as two additional galaxy samples generated from a SAM and from TNG-300. We demonstrate that CS-SHAM reliably reproduces galaxy clustering whether $M_{\mathrm{peak}}$ or $V_{\mathrm{peak}}$ is used as the subhalo mass proxy. We also find that the models are unable to place robust constraints on $f_{\mathrm{sat}}$ if different mass proxies are employed. Indeed, within the CS-SHAM framework the halo occupation distribution (HOD) and conditional luminosity or stellar mass function (CLF/CSMF) are accurately recovered. Furthermore, we demonstrate for the first time that galaxy clustering constrains the HOD and CLF/CSMF primarily for relatively massive halos. Because the halo bias is nearly constant for low-mass halos, galaxy clustering is generally not very sensitive to the satellite population residing in these low-mass systems.