Star formation in NGC 5194 (M51a): The panchromatic view from Galex to Spitzer

D. Calzett, R.C. C. Kennicutt, L. Bianchi, D.A. A. Thilker, D.A. A. Dale, C.W. W. Engelbracht, C. Leitherer, Martin Meyer, M.L. L. Sosey, M. Mutchler, M.W. W. Regan, M.D. D. Thornley, L. Armus, G.J. J. Bendo, S. Boissier, A. Boselli, B.T. T. Draine, K.D. D. Gordon, G. Helou, D.J. J. HollenbachL. Kewley, B.F. F. Madore, D.C. C. Martin, E.J. J. Murphy, G.H. H. Rieke, M.J. J. Rieke, H. Roussel, K. Sheth, J.D. D. Smith, F. Walter, B.A. A. White, S. Yi, N.Z. Z. Scoville, M. Polletta, D. Lindler

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314 Citations (Scopus)


Far-ultraviolet to far-infrared images of the nearby galaxy NGC 5194 (M51a), from a combination of space-based (Spitzer, GALEX, and Hubble Space Telescope) and ground-based data, are used to investigate local and global star formation and the impact of dust extinction. The Spitzer data provide unprecedented spatial detail in the infrared, down to sizes ~500 pc at the distance of NGC 5194. The multiwavelength set is used to trace the relatively young stellar populations, the ionized gas, and the dust absorption and emission in H II-emitting knots, over 3 orders of magnitude in wavelength range. As is common in spiral galaxies, dust extinction is high in the center of the galaxy (Av ~ 3.5 mag), but its mean value decreases steadily as a function of galactocentric distance, as derived from both gas emission and stellar continuum properties. In the IR/UV-UV color plane, the NGC 5194 H II knots show the same trend observed for normal star-forming galaxies, having a much larger dispersion (~ 1 dex peak to peak) than starburst galaxies. We identify the dispersion as due to the UV emission predominantly tracing the evolved, nonionizing stellar population, up to ages ~50-100 Myr. While in starbursts the UV light traces the current star formation rate (SFR), in NGC 5194 it traces a combination of current and recent past SFRs. Possibly, mechanical feedback from supernovae is less effective at removing dust and gas from the star formation volume in normal star-forming galaxies than in starbursts because of the typically lower SFR densities in the former. The application of the starburst opacity curve for recovering the intrinsic UV emission (and deriving SFRs) in local and distant galaxies appears therefore appropriate only for SFR densities ?1 M? yr-1 kpc-2. Unlike the UV emission, the monochromatic 24 µm luminosity is an accurate local SFR tracer for the 24 µm knots in NGC 5194, with a peak-to-peak dispersion of less than a factor of 3 relative to hydrogen emission line tracers; this suggests that the 24 µm emission carrie
Original languageEnglish
Pages (from-to)871-893
Number of pages23
JournalThe Astrophysical Journal
Issue number2 I
Publication statusPublished - 2005


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