MOSEL Survey: JWST Reveals Major Mergers/strong Interactions Drive the Extreme Emission Lines in the Early Universe

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 utilize 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^-1) 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 the control sample. Even after comparing with a stellar mass and stellar mass plus specific star formation rate (SFR)-matched control sample, EELGs have 3 to 5 times higher mass ratios than 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 overabundance of EELGs at z > 6.