The Munich Near-Infrared Cluster Survey.: II.: The K-band luminosity function of field galaxies to z ∼ 1.2

We present a measurement of the evolution of the rest-frame K-band luminosity function to z similar to 1.2 using a sample of more than 5000 K-selected galaxies drawn from the Munich Near- Infrared Cluster Survey (MUNICS) data set. Distances and absolute K-band magnitudes are derived using photometric redshifts from spectral energy distribution fits to BVRIJK photometry. These are calibrated using more than 500 spectroscopic redshifts. We obtain redshift estimates having an rms scatter of 0.055 and no mean bias. We use Monte Carlo simulations to investigate the influence of the errors in distance associated with photometric redshifts on our ability to reconstruct the shape of the luminosity function. Finally, we construct the rest-frame K-band LF in four redshift bins spanning 0.4 < z < 1.2 and compare our results to the local luminosity function. We discuss and apply two different estimators to derive likely values for the evolution of the number density, Phi*, and characteristic luminosity, M*, with redshift. While the first estimator relies on the value of the luminosity function binned in magnitude and redshift, the second estimator uses the individually measured {M, z} pairs alone. In both cases we obtain a mild decrease in number density by similar to25% to z = 1, accompanied by brightening of the galaxy population by 0.5 - 0.7 mag. These results are fully consistent with an analogous analysis using only the spectroscopic MUNICS sample. The total K-band luminosity density is found to scale as d log rhoL/dz = 0.24. We discuss possible sources of systematic errors and their influence on our parameter estimates. By comparing the luminosity density and the cumulative redshift distributions of galaxies in single survey fields to the sample averages, we show that cosmic variance is likely to significantly influence infrared selected samples on scales of similar to 100 arcmin(2).