The evolution of star formation rates in high-redshift galaxies

Abstract

We use photometric galaxy samples and spectral synthesis models to investigate the ability of three dramatically divergent star formation histories (SFHs) to describe the build-up of stellar mass in galaxy populations between z∼5 and z∼2. The SFHs in question assume constant, exponentially increasing, and exponentially decreasing star formation rates (SFRs). For each considered SFH, we use a broadband spectral energy distribution model-fitting technique to parameterize the galaxy samples according to photometric redshift, color excess, age, stellar mass, and SFR. Starting at z∼5, we then evolve the stellar mass and SFR of a toy galaxy across the epochs in question and quantify its agreement with the model-fit observations at z∼3 and z∼2. This is done for each assumed SFH. We find the exponentially increasing SFH with a 500 Myr e-folding agrees best with the model-fit observations, while the exponentially decreasing SFH shows the worst agreement. We further analyze the model-fit data for trends in color excess versus rest-frame UV magnitude and identify that, for z∼3 galaxies fit for constant star formation, UV-brighter objects are more highly obscured by dust than the UV-faint. This dependence is not identified in the other data sets.