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|Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies|
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
|Galaxy Properties at the North Galactic Pole. I. Photometric Properties on Large Spatial Scales|
A two-color study of the galaxies detected on POSS-I in a 289 squaredegree region centered on the North Galactic Pole is presented. We use avariety of mapping techniques to characterize the large-scale spatialdistribution of galaxies. The depth and sample size of this new surveyallows, for the first time, the isolation of large photometricsubsamples of galaxies in high- and low-density environments on thescale of superclusters. Our principal finding is a statisticallysignificant difference between the mean photometric properties of thesesubsamples in the sense that galaxies in the high-density Coma andfilament environments have redder colors and larger concentrationindices than galaxies drawn from low-density interfilament regions.These results are in accord with the known morphology-density relation.Thus, appropriately chosen photometric and morphological parameters, inconcert with a galaxy surface density map, can be used to selectstructures from the projected galaxy distribution which correspond toregions of high density. An illustration of this point is our discoveryof a concentration of blue galaxies identified in our maps near the coreof the Coma cluster. This feature is comprised of early-type galaxieswhich exhibit signs of current or recent star formation. These resultsare predicated on relations between morphological type and photometricparameters derived from APS scans of POSS-I. We therefore discuss theimage calibration procedures used to compile our catalog of physicallysignificant photometric parameters. We demonstrate the morphologicaltype dependence among quantities such as mean color and imageconcentration index, and the lack of such a dependence for mean surfacebrightness.
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