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

Abstract

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^-2_100 M_⊙ yr^-1 (q_0 = 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 ~10^9 h^-2_100 M_⊙ of stars, or ~1/20 of the stellar mass of a present-day L^* galaxy. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555. Based on observations made at the Kitt Peak National Observatory, National Optical Astronomy Observatories, operated by AURA, Inc., under cooperative agreement with the National Science Foundation.