Optical-IR spectral energy distribution of the protogalaxy candidate MS 1512-cB58

The spectral energy distribution of the protogalaxy candidate MS 1512-cB58 at z = 2.72 is presented. Photometry in seven bands ranging from g to K' (1300-6000 A rest wavelength) are fitted with population synthesis models. The data confirm a very young age for this galaxy in agreement with ages estimated from preliminary C IV λ1550 P Cygni profile modeling. Single-burst models with ages greater than about 20 Myr can be discarded at the 99% confidence level, and continuous star formation models with ages greater than about 35 Myr can be discarded at the 95% confidence level. The spectral energy distribution is most consistent with a continuous star formation model of about 10-20 Myr, with reddening of E(B-V) ∼ 0.3. No evidence for an older population of stars is seen, but the possibility of an older population with as much as 90% of the galaxy mass cannot be ruled out. We discuss the possible ramifications of a nonstandard IMF and gravitational lensing on the galaxy's age and mass.