2024ApJ...975..238N

Recent JWST observations with superb angular resolution have revealed the existence of clumpy galaxies at high redshift through the detection of rest-frame optical emission lines. We use the FirstLight simulation to study the properties of (sub)galactic clumps that are bright in the [O III] λ5007 line with flux greater than ∼10^–18 erg s^–1 cm^–2, to be detected by JWST. For 62 simulated galaxies that have stellar masses of (0.5-6) × 10¹⁰M_⊙ at z = 5, we find clumps in 1828 snapshots in the redshift range z = 9.5-5.5. The clumps are identified by the surface density of the star formation rate (SFR). About one-tenth of the snapshots show the existence of clumpy systems with two or more components. Most of the clumps are formed by mergers and can be characterized by their ages: central clumps dominated by stellar populations older than 50 Myr, and off-centered clumps dominated by younger stellar populations with specific SFRs of ∼50 Gyr^–1. The latter type of young clumps is formed from gas debris in the tidal tails of major mergers with baryonic mass ratios of 1 ≤ q < 4. The merger-induced clumps are short-lived and merge within a dynamical time of several tens of million years. The number density of the clumpy systems is estimated to be ∼10^–5 cMpc^–3, which is large enough to be detected in recent JWST surveys.