The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: exploring the Halo Occupation Distribution model for Emission Line Galaxies

TL;DR

This study models the Halo Occupation Distribution for emission line galaxies in eBOSS DR16, analyzing how various physical assumptions affect galaxy clustering statistics and providing publicly available galaxy catalogues.

Contribution

It introduces a comprehensive HOD modeling framework for ELGs, considering multiple physical effects and their impact on clustering, with implications for cosmological measurements.

Findings

The projected correlation function is sensitive to satellite and PDF assumptions.

The quadrupole is mainly affected by velocity profile choices.

HOD shape has a subdominant impact on clustering results.

Abstract

We study the modelling of the Halo Occupation Distribution (HOD) for the eBOSS DR16 Emission Line Galaxies (ELGs). Motivated by previous theoretical and observational studies, we consider different physical effects that can change how ELGs populate haloes. We explore the shape of the average HOD, the fraction of satellite galaxies, their probability distribution function (PDF), and their density and velocity profiles. Our baseline HOD shape was fitted to a semi-analytical model of galaxy formation and evolution, with a decaying occupation of central ELGs at high halo masses. We consider Poisson and sub/super-Poissonian PDFs for satellite assignment. We model both NFW and particle profiles for satellite positions, also allowing for decreased concentrations. We model velocities with the virial theorem and particle velocity distributions. Additionally, we introduce a velocity bias and a net infall velocity. We study how these choices impact the clustering statistics while keeping the number density and bias fixed to that from eBOSS ELGs. The projected correlation function, $w_p$, captures most of the effects from the PDF and satellites profile. The quadrupole, $\xi_2$, captures most of the effects coming from the velocity profile. We find that the impact of the mean HOD shape is subdominant relative to the rest of choices. We fit the clustering of the eBOSS DR16 ELG data under different combinations of the above assumptions. The catalogues presented here have been analysed in companion papers, showing that eBOSS RSD+BAO measurements are insensitive to the details of galaxy physics considered here. These catalogues are made publicly available.