Optical-Infrared Spectral Energy Distributions of z > 2 Lyman Break Galaxies

Broadband optical and IR spectral energy distributions are determined for spectroscopically confirmed z > 2 Lyman break objects in the Hubble Deep Field (HDF). These photometric data are compared with spectral synthesis models which take into account the effects of metallicity and of internal reddening due to dust. It is found that, on average, Lyman break objects are shrouded in enough dust [typically E(B - V) ≈ 0.3] to suppress their UV fluxes by a factor of more than 10. The dust-corrected star formation rate in a typical HDF Lyman break object is ~60 h M⊙ yr-1 (q0 = 0.5). Furthermore, these objects are dominated by very young (0.2 Gyr, and a median of ~25 Myr) stellar populations, suggesting that star formation at high redshift is episodic rather than continuous. Typically, these star formation episodes produce ~109 h M⊙ of stars, or ~1/20 of the stellar mass of a present-day L* galaxy.

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