Modeling Galaxy Colors with Stochastic Star Formation Histories

Using stellar population synthesis, we construct a model for the distribution of high-redshift galaxies on the UVJ diagram, i.e. the rest-frame U-V vs V-J plane. We find that stochastic star formation history models are able to reproduce the observed color distributions of star-forming galaxies, when combined with the assumption of a random distribution of dust attenuation values across the galaxy population. This may indicate that galaxy inclinations are a major contributor to the observed UVJ distribution. We confirm this hypothesis using a simple geometric model, where the dust attenuation for each galaxy is uniquely determined by the viewing angle, total amount of dust, and disk thickness. We also find that the color distribution is substantially different for low- and high-mass galaxies. This can be explained by a systematic change in the disk thickness, where the most massive galaxies are almost spheroidal, and consequently have the smallest spread in dust attenuation.

The SAO REU program is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no. AST-1852268, and by the Smithsonian Institution.