Spitzer Survey of Stellar Structure in Galaxies (S$^4$G). The Pipeline
  4: Multi-component decomposition strategies and data release
  The Spitzer Survey of Stellar Structure in Galaxies (S$^4$G, Sheth et. al.
2010) is a deep 3.6 and 4.5 $\mu$m imaging survey of 2352 nearby ($< 40$ Mpc)
galaxies. We describe the S$^4$G data analysis pipeline 4, which is dedicated
to 2-dimensional structural surface brightness decompositions of 3.6 $\mu$m
images, using GALFIT3.0 \citep{peng2010}. Besides automatic 1-component
S\'ersic fits, and 2-component S\'ersic bulge + exponential disk fits, we
present human supervised multi-component decompositions, which include, when
judged appropriate, a central point source, bulge, disk, and bar components.
Comparison of the fitted parameters indicates that multi-component models are
needed to obtain reliable estimates for the bulge S\'ersic index and
bulge-to-total light ratio ($B/T$), confirming earlier results
\citep{laurikainen2007, gadotti2008, weinzirl2009}. In this first paper, we
describe the preparations of input data done for decompositions, give examples
of our decomposition strategy, and describe the data products released via IRSA
and via our web page ({\bf \tt www.oulu.fi/astronomy/S4G\_PIPELINE4/MAIN}).
These products include all the input data and decomposition files in electronic
form, making it easy to extend the decompositions to suit specific science
purposes. We also provide our IDL-based visualization tools (GALFIDL) developed
for displaying/running GALFIT-decompositions, as well as our mask editing
procedure (MASK\_EDIT) used in data preparation. In the second paper we will
present a detailed analysis of the bulge, disk, and bar parameter derived from
multi-component decompositions.
