Assessing the Predictive Power of Galaxy Formation Models: a Comparison of Predicted and Observed Rest-frame Optical Luminosity Functions

Recent galaxy formation models successfully reproduce the local luminosity function (LF) of galaxies, by invoking mechanisms to suppress star formation in lowand high-mass galaxies. As these models are optimized to fit the LF at low redshift, a crucial question is how well they predict the LF at earlier times. Here we compare recently measured rest-frame V -band LFs of galaxies at redshifts 2.0 ≤ z ≤ 3.3 to predictions of semi-analytic models by De Lucia & Blaizot (2007) and Bower et al. (2006), and hydrodynamic simulations by Davé et al. (2006). The models succeed for some luminosity and redshift ranges, and fail for others. A notable success is that the Bower et al. model provides a good match to the observed LF at z ∼ 3. However, all models predict an increase with time of the rest-frame V -band luminosity density, whereas the observations show a decrease. The models also have difficulty matching the observed rest-frame colors of galaxies. In all models the luminosity density of red galaxies increases sharply from z ∼ 3 to z ∼ 2.2, whereas it is approximately constant in the observations. Conversely, in the models the luminosity density of blue galaxies is approximately constant whereas it decreases in the observations. These discrepancies cannot be entirely remedied by changing the treatment of dust, and suggest that current models do not yet provide a complete description of galaxy formation and evolution since z ∼ 3. Subject headings: galaxies: evolution — galaxies: formation — galaxies: fundamental parameters — galaxies: high-redshift — galaxies: luminosity function, mass function