  IRAC excels at detecting distant objects. Due to a combination of the shapes
of the spectral energy distributions of galaxies and the low background
achieved from space, IRAC reaches greater depth in comparable exposure time at
3.6 and 4.5 micron than any ground- or space-based facility currently can at
2.2 micron. Furthermore, the longer wavelengths probed by IRAC enable studies
of the rest-frame optical and near-infrared light of galaxies and AGN to much
higher redshift than is possible from the ground. This white paper explores the
merits of different survey strategies for studying the distant universe during
the warm mission. A three-tiered approach serves a wide range of science goals
and uses the spacecraft effectively: 1) an ultra-deep survey of ~0.04 square
degrees to a depth of ~250 hrs (in conjunction with an HST/WFC3 program), to
study the Universe at 7<z<14; 2) a survey of ~2 square degrees to the GOODS
depth of 20 hrs, to identify luminous galaxies at z>6 and characterize the
relation between the build-up of dark matter halos and their constituent
galaxies at 2<z<6, and 3) a 500 square degree survey to the SWIRE depth of 120
s, to systematically study large scale structure at 1<z<2 and characterize high
redshift AGN. One or more of these programs could conceivably be implemented by
the SSC, following the example of the Hubble Deep Field campaigns. As
priorities in this field continuously shift it is also crucial that a fraction
of the exposure time remains unassigned, thus enabling science that will
reflect the frontiers of 2010 and beyond rather than those of 2007.
