Rest-Frame Ultraviolet to Near-Infrared Observations of an Interacting Lyman Break Galaxy at z = 4.42

We present the rest-frame ultraviolet through near-infrared spectral energy distribution for an interacting Lyman break galaxy at a redshift z = 4.42, the highest redshift merging system known with clearly resolved tidal features. The two objects in this system, HDF-G4 and its previously unidentified companion, are both B₄₃₅-band dropouts, have similar V₆₀₆ − i₇₇₅ and i₇₇₅ − z₈₅₀ colors, and are separated by 1'', which at z = 4.42 corresponds to 7 kpc projected nuclear separation; these are all indicators of an interacting system. Fits to stellar population models indicate a stellar mass of M_⋆ = 2.6 × 10¹⁰ M_☉, an age of τ_⋆ = 720 Myr, and an exponential star formation history, with an e-folding time τ₀ = 440 Myr. Using these derived stellar populations as constraints, we model the HDF-G4 system using hydrodynamical simulations, and find that it will likely evolve into a quasar by z ∼ 3.5, and a quiescent, compact spheroid by z ∼ 2.5, similar to those observed at z≳ 2. The existence of such an object supports galaxy formation models in which major mergers drive the high-redshift buildup of spheroids and black holes.