The DESI One-Percent Survey: A concise model for galactic conformity of ELGs

TL;DR

This paper introduces a simple yet effective model to better understand the clustering and conformity of emission line galaxies (ELGs) in the DESI survey, improving the ELG-halo connection and matching observed auto correlations.

Contribution

A concise conformity model based on subhalo abundance matching that boosts satellite ELGs in halos with ELG centrals, accurately reproducing small-scale clustering data.

Findings

Successfully reproduces ELG auto correlations on small scales.

Model remains consistent with observed cross correlations with LRGs.

Applicable across redshifts from 0.8 to 1.6.

Abstract

Galactic conformity is the phenomenon in which a galaxy of a certain physical property is correlated with its neighbors of the same property, implying a possible causal relationship. The observed auto correlations of emission line galaxies (ELGs) from the highly complete DESI One-Percent survey exhibit a strong clustering signal on small scales, providing clear evidence for the conformity effect of ELGs. Building upon the original subhalo abundance matching (SHAM) method developed by Gao et al. (2022, 2023), we propose a concise conformity model to improve the ELG-halo connection. In this model, the number of satellite ELGs is boosted by a factor of $\sim 5$ in the halos whose central galaxies are ELGs. We show that the mean ELG satellite number in such central halos is still smaller than 1, and the model does not significantly increase the overall satellite fraction. With this model, we can well recover the ELG auto correlations to the smallest scales explored with the current data (i.e. $r_{\mathrm{p}} > 0.03$ $\mathrm{Mpc}\,h^{-1}$ in real space and at $s > 0.3$ $\mathrm{Mpc}\,h^{-1}$ in redshift space), while the cross correlations between luminous red galaxies (LRGs) and ELGs are nearly unchanged. Although our SHAM model has only 8 parameters, we further verify that it can accurately describe the ELG clustering in the entire redshift range from $z = 0.8$ to $1.6$. We therefore expect that this method can be used to generate high-quality ELG lightcone mocks for DESI.