Unraveling emission line galaxy conformity at z~1 with DESI early data

TL;DR

This paper investigates the properties and clustering behavior of emission line galaxies at z~1, revealing their merger-driven star formation and the importance of including galaxy conformity in models for accurate cosmological analysis.

Contribution

It introduces a physical model of ELGs, highlights the role of galaxy conformity, and emphasizes the need to incorporate conformity effects into ELG-halo connection modeling.

Findings

ELGs are rapidly star-forming, often merger-driven galaxies.

Conformity leads to correlated star formation in central-satellite ELG pairs.

Inclusion of conformity improves ELG clustering models.

Abstract

Emission line galaxies (ELGs) are now the preeminent tracers of large-scale structure at z>0.8 due to their high density and strong emission lines, which enable accurate redshift measurements. However, relatively little is known about ELG evolution and the ELG-halo connection, exposing us to potential modeling systematics in cosmology inference using these sources. In this paper, we propose a physical picture of ELGs and improve ELG-halo connection modeling using a variety of observations and simulated galaxy models. We investigate DESI-selected ELGs in COSMOS data, and infer that ELGs are rapidly star-forming galaxies with a large fraction exhibiting disturbed morphology, implying that many of them are likely to be merger-driven starbursts. We further postulate that the tidal interactions from mergers lead to correlated star formation in central-satellite ELG pairs, a phenomenon dubbed "conformity." We argue for the need to include conformity in the ELG-halo connection using galaxy models such as IllustrisTNG, and by combining observations such as the DESI ELG auto-correlation, ELG cross-correlation with Luminous Red Galaxies (LRGs), and ELG-cluster cross-correlation. We also explore the origin of conformity using the UniverseMachine model and elucidate the difference between conformity and the well-known galaxy assembly bias effect.