The Munich Near-Infrared Cluster Survey: Number density evolution of massive field galaxies to z similar to 1.2 as derived from the K-band-selected survey

We derive the number density evolution of massive field galaxies in the red shift range using the 0.4 < z < 1.2 K-band-selected field galaxy sample fro m the Munich Near-IR Cluster Survey. We rely on spectroscopically calibrate d photometric redshifts to determine distances and absolute magnitudes in t he rest-frame K band. To assign mass-to-light ratios, we use an approach th at maximizes the stellar mass for any K-band luminosity at any redshift. We take the mass-to-light ratio, M/L-K, of a simple stellar population that i s 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 r ealistic model M/L-K will probably decrease faster with redshift because of increased star formation. We compute the number density of galaxies more m assive than 2 x 10(10), 5 x 10(10), and 1 x 10(11) h(-2) M-., finding that the integrated stellar mass function is roughly constant for the lowest mas s limit and that it decreases with redshift by a factor of similar to3 and by a factor of similar to6 for the two higher mass limits, respectively. Th is finding is in qualitative agreement with models of hierarchical galaxy f ormation, which predict that the number density of similar toM(*) objects i s fairly constant while it decreases faster for more massive systems over t he redshift range that our data set probes.