GALAXY PROPERTIES AT THE NORTH GALACTIC POLE .1. PHOTOMETRIC PROPERTIES ON LARGE SPATIAL SCALES

A two-color study of the galaxies detected on POSS-I in a 289 square d egrees region centered on the North Galactic Pole is presented. We use a variety of mapping techniques to characterize the large-scale spati al distribution of galaxies. The depth and sample size of this new sur vey allows, for the first time, the isolation of large photometric sub samples of galaxies in high- and low-density environments on the scale of superclusters. Our principal finding is a statistically significan t difference between the mean photometric properties of these subsampl es in the sense that galaxies in the high-density Coma and filament en vironments have redder colors and larger concentration indices than ga laxies drawn from low-density interfilament regions. These results are in accord with the known morphology-density relation. Thus, appropria tely chosen photometric and morphological parameters, in concert with a galaxy surface density map, can be used to select structures from th e projected galaxy distribution which correspond to regions of high de nsity. An illustration of this point is our discovery of a concentrati on of blue galaxies identified in our maps near the core of the Coma c luster. This feature is comprised of early-type galaxies which exhibit signs of current or recent star formation. These results are predicat ed on relations between morphological type and photometric parameters derived from APS scans of POSS-I. We therefore discuss the image calib ration procedures used to compile our catalog of physically significan t photometric parameters. We demonstrate the morphological type depend ence among quantities such as mean color and image concentration index , and the lack of such a dependence for mean surface brightness. (C) 1 995 American Astronomical Society.