Ultradeep IRAC Imaging Over The HUDF And GOODS-South: Survey Design And
  Imaging Data Release
  The IRAC ultradeep field (IUDF) and IRAC Legacy over GOODS (IGOODS) programs
are two ultradeep imaging surveys at 3.6{\mu}m and 4.5{\mu}m with the Spitzer
Infrared Array Camera (IRAC). The primary aim is to directly detect the
infrared light of reionization epoch galaxies at z > 7 and to constrain their
stellar populations. The observations cover the Hubble Ultra Deep Field (HUDF),
including the two HUDF parallel fields, and the CANDELS/GOODS-South, and are
combined with archival data from all previous deep programs into one ultradeep
dataset. The resulting imaging reaches unprecedented coverage in IRAC 3.6{\mu}m
and 4.5{\mu}m ranging from > 50 hour over 150 arcmin^2, > 100 hour over 60 sq
arcmin2, to 200 hour over 5 - 10 arcmin$^2$. This paper presents the survey
description, data reduction, and public release of reduced mosaics on the same
astrometric system as the CANDELS/GOODS-South WFC3 data. To facilitate
prior-based WFC3+IRAC photometry, we introduce a new method to create high
signal-to-noise PSFs from the IRAC data and reconstruct the complex spatial
variation due to survey geometry. The PSF maps are included in the release, as
are registered maps of subsets of the data to enable reliability and
variability studies. Simulations show that the noise in the ultradeep IRAC
images decreases approximately as the square root of integration time over the
range 20 - 200 hours, well below the classical confusion limit, reaching
1{\sigma} point source sensitivities as faint as of 15 nJy (28.5 AB) at
3.6{\mu}m and 18 nJy (28.3 AB) at 4.5{\mu}m. The value of such ultradeep IRAC
data is illustrated by direct detections of z = 7 - 8 galaxies as faint as HAB
= 28.
