Evolution in the colors of lyman break galaxies from z 4 to z 3
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The integrated colors of distant galaxies provide a means for interpreting the properties of their stellar content. Here we use rest-frame UV-to-optical colors to constrain the spectral energy distributions and stellar populations of color-selected, B-dropout galaxies at z 4 in the Great Observatories Origins Deep Survey (GOODS). We combine the Advanced Camera for Surveys data with ground-based near-infrared images, which extend the coverage of galaxies at z 4 to the rest-frame B band. We observe a color-magnitude trend in the rest-frame m(UV)-B versus B diagram for the z 4 galaxies that has a fairly well-defined "blue envelope," and is strikingly similar to that of color-selected, U-dropout galaxies at z 3. We also find that although the co-moving luminosity density at rest-frame UV wavelengths (1600 ) is roughly comparable at z 3 and 4, the luminosity density at rest-frame optical wavelengths increases by about one-third from z 4 to 3. Although the star formation histories of individual galaxies may involve complex and stochastic events, the evolution in the global luminosity density of the UV-bright galaxy population corresponds to an average star formation history with a star formation rate that is constant or increasing over these redshifts. This suggests that the evolution in the luminosity density corresponds to an increase in the stellar mass density of 33%.
