The Spitzer Survey of Stellar Structure in Galaxies (S4G)


The Spitzer Survey of Stellar Structure in Galaxies (S⁴G) is a volume-, magnitude-, and size-limited survey of over 2300 nearby galaxies at 3.6 and 4.5μm.  This is an extremely deep survey reaching an unprecedented 1σ surface brightness limit of μ3.6μm(AB) = 27 mag arcsec-2. This translates to a stellar surface density of << 1 M pc-2

S⁴G can thus probe the stellar structure in galaxies in a regime where the gas dominates the stars (typical HI surface density ~ a few M pc-2).

In the three years prior to the data release, the S⁴G team operated under a novel policy to freely share data and maximize scientific return.  As of the Jan 2013, the  data and basic science products have been released to the community and therefore the policy is no longer in place.  However, an enhanced effort in the form of a European Union-funded Initial Training Network called DAGAL (PI Johan Knapen) to exploit S⁴G using additional data is now underway.


Galaxies are the basic building blocks of the Universe, and understanding their formation and evolution is crucial to many areas of current astrophysical research. Nearby galaxies, being the 'fossil record' of the evolution of galaxies, provide a wealth of detail to test extensively the current models of galaxy formation and evolution. A galaxy's structure is linked to both its mass and evolution history. Probing galactic structure requires understanding the distribution of stars among galaxies of all types and luminosities across the full range of environments.

This was the motivation for S⁴G.  It is a representative, volume-limited (d < 40 Mpc) survey of nearby spiral, elliptical, and dwarf galaxies at 3.6 and 4.5μm designed to address fundamental questions of galactic structure that are united by the common need for deep, uniform, unbiased maps of the stellar mass in galaxies