A near-infrared faint galaxy survey : evolution and the cosmological geometry from K band photometry

Abstract

The results of four K band surveys of the extragalactic sky are presented. Each survey was designed to balance depth with area of coverage, and a sufficient number of galaxies was studied at each magnitude from K=12 to K=22 to provide good statistics. Each survey area was also observed in the B and I bands. Methods for making long exposures in the near-infrared and optical are described. The K band number counts are compiled. The excess seen in the B band number counts is not seen in the K band number counts, and a change in slope is seen in the K counts at K=17. The number count data are shown to be consistent with the measured B-K color, as the K band selected sample becomes rapidly bluer after turning over at K=17. The I-K colors are presented and it is argued that there is a deficiency of galaxies with the colors of unevolved ell1pticalsat z = 1. The B-K colors are shown to move away from the no-evolution model beginning at K = 17. The position of the galaxies on the B-1 vs I-K plot are consistent with these arguments. The surface brightness of the galaxies is analyzed and it is argued that variation in surface brightness causes no systematic bias in the number count data. Various aspects of the data are compared with models of primeval galaxies and galaxy evolution. The K band number counts are compared with a model of pure luminosity evolution, a cosmological constant model and a merging model. It is argued that the merging model is the best explanation for all of the data, although the model needs to be modified before it will provide a good fit to the number counts.