The Spitzer Survey of Stellar Structure in Galaxies (S^4G)
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°,m_(Bcorr) < 15:5, and D_(25) > 1') survey of 2331 galaxies using the Infrared Array Camera (IRAC) at 3.6 and 4.5 μm. Each galaxy is observed for 240 s and mapped to ≥ 1:5 × D_(25). The final mosaicked images have a typical 1 σ rms noise level of 0.0072 and 0:0093 MJy sr^-1 at 3.6 and 4.5 μm, respectively. Our azimuthally averaged surface brightness profile typically traces isophotes at μ_(3.6μm (AB)(1σ) ~ 27 mag arcsec^(-2), equivalent to a stellar mass surface density of ~1 M_⊙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 large, unbiased, and extremely deep sample of all Hubble types from dwarfs to spirals to ellipticals will allow for detailed structural studies, not only as a function of stellar mass, but also as a function of the local environment. The data from this survey will serve as a vital testbed for cosmological simulations predicting the stellar mass properties of present-day galaxies. This article introduces the survey and describes the sample selection, the significance of the 3.6 and 4.5 μm bands for this study, and the data collection and survey strategies. We describe the S^4G data analysis pipeline and present measurements for a first set of galaxies, observed in both the cryogenic and warm mission phases of Spitzer. For every galaxy we tabulate the galaxy diameter, position angle, axial ratio, inclination at μ_(3.6μm)(AB) = 25:5, and 26:5 mag arcsec^(-2) (equivalent to ≈μ_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, using the galaxy-fitting code GALFIT, we deconstruct each galaxy 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 and will enable a variety of scientific investigations, some of which are highlighted in this introductory S^4G survey paper.
© 2010 The Astronomical Society of the Pacific. Received 2010 April 22; accepted 2010 October 6; published 2010 December 2. The authors thank the referee for useful comments and suggestions that greatly helped improve this article. We are also grateful to the dedicated staff at the Spitzer Science Center for their support and help with the planning and execution of this legacy exploration program. K. S. would like to thank L. Armus, E. Bell, S. Carey, E. Churchwell, M. Dickinson, G. Helou, N. Scoville, and J. Stauffer for sharing their experiences in leading large teams. A. G. d. P. and J. C. M. M. are partially financed by the Spanish Programa Nacional de Astronomía y Astrofísica under grants AyA2006-02358 and AyA2009-10368. A. G. d. P. is also financed by the Spanish Ramón y Cajal program. J. C. M. M. acknowledges the receipt of a Formación del Profesorado Universitario fellowship. E. L. and H. S. acknowledge support from the Academy of Finland. K. M. D. is supported by a National Science Foundation (NSF) Astronomy and Astrophysics Postdoctoral Fellowship under award AST-0802399. D. M. E. acknowledges support from the Spitzer Science Center from NASA grant JPL RSA-1368024. R. B. acknowledges support from NSF grant AST 05-07140. E. A. and A. B. thank the Centre National d'Etudes Spatiales and ANR-06-BLAN-0172 for support. K. L. M. acknowledges funding from the Peter and Patricia Gruber Foundation as the 2008 IAU Fellow, from the University of Portsmouth, and from the South East Physics Network. This work is based on observations and archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA. We gratefully acknowledge support from NASA JPL/Spitzer grant RSA 1374189 provided for the S^4G project.
Published - Sheth2010p12393Publ_Astron_Soc_Pac.pdf