Description
I present the most comprehensive study of major galaxy mergers (stellar mass ratio 1:4) to date, focusing on the underexplored redshift range of z∼3–9. Using NIRCam imaging and NIRSpec spectroscopic data from the JADES GTO program, I examine galaxy close pair fractions, major merger rates, and mass accretion rates to assess the role of mergers in galaxy growth. Close pair fractions are measured using a probabilistic method that incorporates full posterior distributions and uncertainties from photometric redshifts and spectral energy distribution (SED) fitting for a mass-complete sample in the range of log(M/Msol) = 8–10. Galaxies hosting major companions are identified based on projected 5–30 kpc separations and overlapping redshift posteriors. The redshift evolution of close pair fractions rises steeply and turns over at z∼6, with a dependence on primary galaxy mass. By assuming merger timescales from simulations, these fractions are converted into major merger rates, which increase and flatten at high redshifts, showing weak stellar mass scaling. Cumulative mass accretion from mergers contributes approximately 5-14% to total mass growth, consistent with ex-situ mass fractions from our simple numerical model. Additionally, I evaluate the role of mergers in star formation and stellar mass growth by analysing their position relative to the star-forming main sequence, using SED-derived star formation rates and stellar masses. Finally, I assess the AGN fraction within mergers to explore their connection to triggering AGN activity. This study provides critical insights into the hierarchical growth of galaxies during the early universe.
