Hα Imaging of the Candidate Protogalaxy MS 1512-cB58

摘要

We have obtained an image of the candidate protogalaxy MS 1512-cB58 through a narrow passband filter centered on Hα redshifted to z = 2.72. MS 1512-cB58 shows excess emission that is spatially extended, has a rest equivalent width of 56.7 A, and luminosity of 3 × 10~43 h~-2_75 ergs s~-1 (q_0 = 0.1). Assuming that the excess emission arises from nebular Hα associated with H II regions, the observed luminosity implies a star formation rate of 285 M◎ yr~-1 (neglecting any possible magnification by gravitational lensing). By comparison, the luminosity of the stellar continuum at 1500 A, along with models for the spectral energy distribution, indicate a star formation rate about a factor of 12 greater. We discuss plausible explanations for this discrepancy and possible future observations that may clarify the situation.