2007ApJ...671.1241Y

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_*=2.6x10¹⁰ 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.