The mass profile and shape of bars in the spitzer survey of stellar structure in galaxies (S^(4)G): search for an age indicator for bars
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2015
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IOP Publishing
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Abstract
We have measured the radial light profiles and global shapes of bars using two-dimensional 3.6 μm image decompositions for 144 face-on barred galaxies from the Spitzer Survey of Stellar Structure in Galaxies. The bar surface brightness profile is correlated with the stellar mass and bulge-to-total (B/T) ratio of their host galaxies. Bars in massive and bulge-dominated galaxies (B/T > 0.2) show a flat profile, while bars in less massive, disk-dominated galaxies (B/T ~ 0) show an exponential, disk-like profile with a wider spread in the radial profile than in the bulge-dominated galaxies. The global two-dimensional shapes of bars, however, are rectangular/boxy, independent of the bulge or disk properties. We speculate that because bars are formed out of disks, bars initially have an exponential (disk-like) profile that evolves over time, trapping more disk stars to boxy bar orbits. This leads bars to become stronger and have flatter profiles. The narrow spread of bar radial profiles in more massive disks suggests that these bars formed earlier (z > 1), while the disk-like profiles and a larger spread in the radial profile in less massive systems imply a later and more gradual evolution, consistent with the cosmological evolution of bars inferred from observational studies. Therefore, we expect that the flatness of the bar profile can be used as a dynamical age indicator of the bar to measure the time elapsed since the bar formation. We argue that cosmic gas accretion is required to explain our results on bar profile and the presence of gas within the bar region.
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© 2015. The American Astronomical Society. Artículo firmado por 27 autores. We thank Frederic Bournaud, the referee, for insightful comments that greatly improved this paper. The authors thank the S^(4)G team for their effort in this project. T.K. is grateful to Woong-Tae Kim and his research group for their helpful comments and discussions. T.K., K.S., J.-C.M.-M., and T.M. acknowledge support from the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We are grateful for the support from NASA JPL/Spitzer grant RSA 1374189 provided for the S^(4)G project. T.K. and M.G.L. were supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MEST; No. 2012R1A4A1028713). T.K. acknowledges the support from ESO for the studentship in 2011-2012. D.A.G. acknowledges funding under the Marie Curie Actions of the European Commission (FP7-COFUND). E.A. and A.B. thank the Centre National d'Etudes Spatiales for financial support. We acknowledge financial support from the People Programme (Marie Curie Actions) of the European Union's FP7/2007-2013/ to the DAGAL network under REA grant agreement No. PITN-GA-2011-289313. L.C.H acknowledges support by the Chinese Academy of Science through grant No. XDB09030102 (Emergence of Cosmological Structures) from the Strategic Priority Research Program and by the National Natural Science Foundation of China through grant No. 11473002. This research is based on observations and archival data made with the Spitzer Space Telescope and made use of the NASA/IPAC Extragalactic Database (NED), which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). We acknowledge the usage of the HyperLeda database (http://leda.univ-lyon1.fr).