Observation and reduction methods of deep Palomar 200 inch 4-Shooter mosaics
Lyman W. Neuschaefer, Rogier A. Windhorst · The Astrophysical Journal Supplement Series · 1995
We present deep contiguous CCD-mosaics in Gunn gri filters with the Palomar 200 inch 4-Shooter CCD array for two widely separated survey fields, each ~0.45^deg^ x 0.45^deg^ in size. We used the FOCAS package to compile multicolor catalogs in each survey field that contain ~23,000 galaxies and have 90% completeness limits of gri <~ 24.5 mag (B_J_ <~ 25.2 mag). The purpose is to constrain the evolution of galaxy clustering by tracing w(θ) down to B_J_ ~ 25mag. This paper describes the photometric and astrometric reduction methods of our 4-Shooter mosaics and the resulting faint galaxy catalogs. The accuracy of the global photometric zero points is determined from overlapping 4-Shooter frames and the known colors of field main-sequence stars, and amounts to ~0.08 mag rms. Astrometric solutions are determined from 10-15 secondary standard stars for each CCD with accurately measured coordinates from recent-epoch Palomar 48 inch Schmidt plates. The CCD frame-to-frame overlap shows that the rms accuracy of each CCD's astrometry is <~0.5". Using <~ 8 PSF stars in each CCD, we can distinguish stars from galaxies using object shape parameters down to gri <~ 23 mag. We present the resulting galaxy counts down to Gunn gri <~ 25 mag. The completeness of our galaxy catalogs is determined by comparing our galaxy counts with those from somewhat deeper surveys that cover much smaller areas. The multicolor two-point angular correlation functions for galaxies in these fields are presented in a companion (main journal) paper.