Infrared imaging of high-redshift galaxies.

Abstract

First we present new infrared counts of field galaxies from more than 20 square arcminutes to a limiting magnitude of K = 20 and from 2 square arcminutes to K = 21.5. At the faintest magnitudes the counts are slightly higher than those reported previously, though still consistent given the small numbers of galaxies in the two samples. Next we present models predicting the magnitude, redshift and color distributions of field galaxies. We explore whether a fading starburst scenario can account for the observations of faint blue galaxies. We marginally rule out a starburst scenario with a local IMF because the models predict too many nearby faint galaxies that are not observed. A burst model with a truncated IMF reproduces the counts and redshift distributions well but produces too blue a population. We show that surface brightness selection has a significant effect on the distributions. In particular, adding a population of low-surface brightness galaxies, known to exist locally, can explain the counts for B(J) < 23. Finally we show that the colors of galaxies in a K-band selected sample are not consistent with a passive evolution model. In the final section we consider the effects of radio power on a sample of galaxies around z = 1. We have obtained BRJHK images of 25 galaxies from the MIT-Green Bank (MG) radio survey. Compared with a sample of more powerful 3CR radio galaxies, these galaxies are 0.5 mag fainter when measured in 8" apertures but not noticeably fainter in 4" apertures. This implies that the near environments of galaxies are correlated with radio power. The MG sample contains galaxies that are just as blue as the bluest 3CR galaxies, but the median MG galaxy is slightly redder than the median 3CR galaxy at the same redshift.