Digitized POSS-II: Galaxy Number Counts in Two Colors Over a Multi-Plate Region

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Session 51 -- Instrumentation
Display presentation, Wednesday, 9:20-6:30, Pauley Room

[51.23] Digitized POSS-II: Galaxy Number Counts in Two Colors Over a Multi-Plate Region

N.Weir, S.Djorgovski (Caltech), U.Fayyad (JPL)

We have developed a software system for the reduction and analysis of the Palomar-STScI Digital Sky Survey (cf. {\sl B.A.A.S.} 23, p.~1434, and {\sl B.A.A.S.} 24, pp.~741, 750, and 1139). This system, named SKICAT, uses a number of image processing and machine-learning based modules, and conducts pipeline processing of the plate scans, from raw pixel measurement, object classification, photometric matching of multiple plate images, to high-level catalog database manipulation using an X-windows based GUI. We are now in the process of implementing a variety of tools for the scientific and multivariate statistical analysis of the object catalogs. We will present our initial results on galaxy and star counts in two colors (photographic $J$ and $F$, calibrated to Gunn $g$ and $r$ bands), for a multi-plate region near the north Galactic pole, covering up to 5 Survey fields ($\sim 125$ square degrees), and up to 11 Survey fields ($\sim 275$ square degrees) in a single color. The data have been uniformly calibrated using CCD sequences and plate overlaps over the range $16 < r < 20$, within which we are over 90\% complete. We also performed extensive tests to assure the accuracy of automatic galaxy classifications over this magnitude range. Previous results from the southern APM Survey implied dramatic evolution of galaxies at low redshift. We will present our new galaxy counts as function of magnitudes colors in the context of these measurements and galaxy evolution models.

{\sl Acknowledgements:} The POSS-II is partially funded by grants to Caltech from the Eastman Kodak Co., the National Geographic Society, the Samuel Oschin Foundation, the NSF grants AST 84-08225 and AST 87-19465, and the NASA grants NGL 05002140 and NAGW 1710. NW was supported in part by a NSF graduate fellowship and by IPAC. SD acknowledges a partial support from the NASA contract NAS5-31348, the NSF PYI award AST-9157412, the Caltech President's fund, and JPL. Work at JPL is performed under a contract with the NASA.

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