Specific star formation rate profiles in nearby spiral galaxies: Quantifying the inside-out formation of disks

© 2007. The American Astronomical Society. J. C. M. M. acknowledges the receipt of a Formación del Profesorado Universitario fellowship from the Spanish Ministerio de Educación y Ciencia. J. C. M. M., A. G. d. P., J. Z., and J. G. are partially financed by the Spanish Programa Nacional de Astronomía y Astrofísica under grant AYA2003-01676. A. G. d. P. is also financed by the MAGPOP EU Marie Curie Research Training Network. We thank the anonymous referee for his/her comments that have significantly improved the paper. This publication makes use of data products from 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. We have made also use of the NASA/IPAC Extragalactic Database ( NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Stimulating conversations with A. Aragón Salamanca are gratefully acknowledged.
We present specific star formation rate (sSFR) radial profiles for a sample of 161 relatively face-on spiral galaxies from the GALEX Atlas of NearbyGalaxies. The sSFR profiles are derived from GALEX and 2MASS (FUV-K) color profiles after a proper SFR calibration of the UV luminosity and K-band mass-to-light ratio are adopted. The (FUV-K) profiles were first corrected for foreground Galactic extinction and later for internal extinction using the ratio of the total-infrared (TIR) to FUV emission. For those objects where TIR-to-FUV ratio radial profiles were not available, the (FUV-NUV) color profiles were used as a measure of the UV slope. The sSFR radial gradients derived from these profiles allow us to quantify the inside-out scenario for the growth of spiral disks for the first time in the local universe. We find a large dispersion in the slope of the sSFR profiles with a slightly positive mean value, which implies a moderate inside-out disk formation. There is also a strong dependency of the value of this slope on the luminosity and size of the disks, with large systems showing a uniform, slightly positive slope in almost all cases and low-luminosity small disks showing a large dispersion with both positive and negative large values. While a majority of the galaxies can be interpreted as forming stars gradually either from inside out or from outside in, a few disks require episodes of enhanced recent growth with scale lengths of the SFR (or gas infall) being significantly larger at present than in the past. We do not find any clear dependence of the sSFR gradient on the environment (local galaxy density or presence of close neighbors).
Ministerio de Educación y Ciencia (MEC), España
Plan Nacional de Astronomía y Astrofísica (MICINN)
MAGPOP EU Marie Curie Research Training Network
National Aeronautics and Space Administration (NASA)
National Science Foundation (NSF), EE.UU.
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
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