MOSEL survey: JWST reveals major mergers/strong interactions drive the extreme emission lines in the early universe

TL;DR

Deep JWST imaging reveals that extreme emission line galaxies in the early universe are predominantly involved in major mergers and strong interactions, which likely trigger their intense emission lines and contribute to their abundance at high redshifts.

Contribution

This study provides new observational evidence linking major mergers and strong interactions to the extreme emission lines in early universe galaxies, using JWST data and simulations.

Findings

EELGs are more likely to be undergoing strong interactions or major mergers.

Companion galaxies around EELGs have higher mass ratios than control samples.

Major mergers may trigger extreme emission lines and influence galaxy evolution at high redshift.

Abstract

Extreme emission line galaxies (EELGs), where nebular emissions contribute 30-40% of the flux in certain photometric bands, are ubiquitous in the early universe (z>6). We utilise deep NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to investigate the properties of companion galaxies (projected distance <40 kpc, |dv|<10,000 km/s) around EELGs at z~3. Tests with TNG100 simulation reveal that nearly all galaxies at z=3 will merge with at least one companion galaxy selected using similar parameters by z=0. The median mass ratio of the most massive companion and the total mass ratio of all companions around EELGs is more than 10 times higher than the control sample. Even after comparing with a stellar mass and stellar mass plus specific SFR-matched control sample, EELGs have three-to-five times higher mass ratios of the brightest companion and total mass ratio of all companions. Our measurements suggest that EELGs are more likely to be experiencing strong interactions or undergoing major mergers irrespective of their stellar mass or specific SFRs. We suspect that gas cooling induced by strong interactions and/or major mergers could be triggering the extreme emission lines, and the increased merger rate might be responsible for the over-abundance of EELGs at z>6.