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Published September 2010 | Published
Journal Article Open

Mid-infrared Galaxy Morphology from the Spitzer Survey of Stellar Structure in Galaxies (S^4G): The Imprint of the De Vaucouleurs Revised Hubble-Sandage Classification System at 3.6 μm

Abstract

Spitzer Space Telescope Infrared Array Camera imaging provides an opportunity to study all known morphological types of galaxies in the mid-IR at a depth significantly better than ground-based near-infrared and optical images. The goal of this study is to examine the imprint of the de Vaucouleurs classification volume in the 3.6 μm band, which is the best Spitzer waveband for galactic stellar mass morphology owing to its depth and its reddening-free sensitivity mainly to older stars. For this purpose, we have prepared classification images for 207 galaxies from the Spitzer archive, most of which are formally part of the Spitzer Survey of Stellar Structure in Galaxies (S^4G), a Spitzer post-cryogenic ("warm") mission Exploration Science Legacy Program survey of 2331 galaxies closer than 40 Mpc. For the purposes of morphology, the galaxies are interpreted as if the images are blue light, the historical waveband for classical galaxy classification studies. We find that 3.6 μm classifications are well correlated with blue-light classifications, to the point where the essential features of many galaxies look very similar in the two very different wavelength regimes. Drastic differences are found only for the most dusty galaxies. Consistent with a previous study by Eskridge et al., the main difference between blue-light and mid-IR types is an ≈1 stage interval difference for S0/a to Sbc or Sc galaxies, which tend to appear "earlier" in type at 3.6 μm due to the slightly increased prominence of the bulge, the reduced effects of extinction, and the reduced (but not completely eliminated) effect of the extreme population I stellar component. We present an atlas of all of the 207 galaxies analyzed here and bring attention to special features or galaxy types, such as nuclear rings, pseudobulges, flocculent spiral galaxies, I0 galaxies, double-stage and double-variety galaxies, and outer rings, that are particularly distinctive in the mid-IR.

Additional Information

© 2010 The American Astronomical Society. Received 2010 March 22; accepted 2010 July 29; published 2010 August 31. We thank the referee for many helpful comments that improved the presentation of this paper. We also thank D. L. Block for additional comments and for pointing us to a useful reference, as well as the other members of the S4G Team for helping to make the project possible. R.B. acknowledges the support of NSF grant AST 05-07140. K.S. acknowledges support from the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. E.A. and A.B. thank the Centre National d'Etudes Spatiales for financial 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 SEPnet (www.sepnet.ac.uk). H.S. and E.L. acknowledge the Academy of Finland for support. J.H.K. acknowledges support by the Instituto de Astrofisica de Canarias (312407). K.M.D. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-0802399. A.G.dP. and J.C.M.M. are partially financed by the Spanish Programa Nacional de Astronomía y Astrofísica under grants AyA2006-02358 and AyA2009-10368, and by the Spanish MEC under the Consolider-Ingenio 2010 Program grant CSD2006-00070: first Science with the GTC. A.G.dP. is also financed by the Spanish Ramón y Cajal program. J.C.M.M. acknowledges the receipt of a Formación del Profesorado Universitario fellowship. S.C. is supported by a KASI Postdoctoral Fellowship. This work is based (in part) on 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 an award issued by JPL/Caltech. Funding for the OSUBSGS was provided by grants from the NSF (grants AST 92-17716 and AST 96-17006), with additional funding from the Ohio State University. Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, NASA, NSF, the U.S. Department of Energy, the Japanese Monbukagakusho, and Max Planck Society. NED is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

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August 19, 2023
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