  The Spitzer Survey of Stellar Structure in Galaxies S^4G is an Exploration
Science Legacy Program approved for the Spitzer post-cryogenic mission. It is a
volume-, magnitude-, and size-limited (d < 40 Mpc, |b| > 30 degrees, m_(Bcorr)
< 15.5, D25>1') survey of 2,331 galaxies using IRAC at 3.6 and 4.5 microns.
Each galaxy is observed for 240 s and mapped to > 1.5 x D25. The final
mosaicked images have a typical 1 sigma rms noise level of 0.0072 and 0.0093
MJy / sr at 3.6 and 4.5 microns, respectively. Our azimuthally-averaged surface
brightness profile typically traces isophotes at mu_3.6 (AB) (1 sigma) ~ 27 mag
arcsec^-2, equivalent to a stellar mass surface density of ~ 1 Msun pc^-2. S^4G
thus provides an unprecedented data set for the study of the distribution of
mass and stellar structures in the local Universe. This paper introduces the
survey, the data analysis pipeline and measurements for a first set of
galaxies, observed in both the cryogenic and warm mission phase of Spitzer. For
every galaxy we tabulate the galaxy diameter, position angle, axial ratio,
inclination at mu_3.6 (AB) = 25.5 and 26.5 mag arcsec^-2 (equivalent to ~ mu_B
(AB) =27.2 and 28.2 mag arcsec^-2, respectively). These measurements will form
the initial S^4G catalog of galaxy properties. We also measure the total
magnitude and the azimuthally-averaged radial profiles of ellipticity, position
angle, surface brightness and color. Finally, we deconstruct each galaxy using
GALFIT into its main constituent stellar components: the bulge/spheroid, disk,
bar, and nuclear point source, where necessary. Together these data products
will provide a comprehensive and definitive catalog of stellar structures, mass
and properties of galaxies in the nearby Universe.
