Andromeda Optical and Infrared Disk Survey I. New Insights in Wide-Field
  Near-IR Surface Photometry
  We present wide-field near-infrared J and Ks images of the Andromeda Galaxy
taken with WIRCam on the Canada-France-Hawaii Telescope (CFHT) as part of the
Andromeda Optical and Infrared Disk Survey (ANDROIDS). This data set allows
simultaneous observations of resolved stars and NIR surface brightness across
M31's entire bulge and disk (within R=22 kpc). The primary concern of this work
is the development of NIR observation and reduction methods to recover a
uniform surface brightness map across the 3x1 degree disk of M31. This
necessitates sky-target nodding across 27 WIRCam fields. Two sky-target nodding
strategies were tested, and we find that strictly minimizing sky sampling
latency does not maximize sky subtraction accuracy, which is at best 2% of the
sky level. The mean surface brightness difference between blocks in our mosaic
can be reduced from 1% to 0.1% of the sky brightness by introducing scalar sky
offsets to each image. The true surface brightness of M31 can be known to
within a statistical zeropoint of 0.15% of the sky level (0.2 mag arcsec sq.
uncertainty at R=15 kpc). Surface brightness stability across individual WIRCam
frames is limited by both WIRCam flat field evolution and residual sky
background shapes. To overcome flat field variability of order 1% over 30
minutes, we find that WIRCam data should be calibrated with real-time sky
flats. Due either to atmospheric or instrumental variations, the individual
WIRCam frames have typical residual shapes with amplitudes of 0.2% of the sky
after real-time flat fielding and median sky subtraction. We present our WIRCam
reduction pipeline and performance analysis here as a template for future
near-infrared observers needing wide-area surface brightness maps with
sky-target nodding, and give specific recommendations for improving photometry
of all CFHT/WIRCam programs. (Abridged)
