The Munich Near-Infrared Cluster Survey: Number Density Evolution of Massive Field Galaxies to [CLC][ITAL]z[/ITAL][/CLC] ∼ 1.2 as Derived from the [ITAL]K[/ITAL]-Band–selected Survey

We derive the number density evolution of massive field galaxies in the redshift range 0.4 < z < 1.2 using the K -band-selected field galaxy sample from the Munich Near-IR Cluster Survey. We rely on spectroscopically calibrated photometric redshifts to determine distances and absolute magnitudes in the rest-frame K band. To assign mass-to-light ratios, we use an approach that maximizes the stellar mass for any K -band luminosity at any redshift. We take the mass-to-light ratio, / L K , of a simple stellar population that is as old as the universe at the galaxy's redshift as a likely upper limit. This is the most extreme case of pure luminosity evolution, and in a more realistic model / L K will probably decrease faster with redshift because of increased star formation. We compute the number density of galaxies more massive than 2 × 10 10 , 5 × 10 10 , and 1 × 10 11 h -2 ☉ , finding that the integrated stellar mass function is roughly constant for the lowest mass limit and that it decreases with redshift by a factor of ~3 and by a factor of ~6 for the two higher mass limits, respectively. This finding is in qualitative agreement with models of hierarchical galaxy formation, which predict that the number density of ~ M * objects is fairly constant while it decreases faster for more massive systems over the redshift range that our data set probes.