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 (MUNICS). 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 two different approaches. First, we use an approach which maximizes the stellar mass for any K-band luminosity at any redshift. We take the mass-to-light ratio of a Simple Stellar Population (SSP) which is as old as the universe at the galaxys redshift as a likely upper limit. Second, we assign each galaxy a mass-to-light ratio by fitting the galaxys colours against a grid of composite stellar population models and taking their M/L. We compute the number density of galaxies more massive than 2 x 10^10 h^-2 Msun, 5 x 10^10 h^-2 Msun, and 1 x 10^11 h^-2 Msun, 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 our data probe.
تحميل البحث