Star formation in NGC 5194 (M51a). II. The spatially resolved star formation law

Robert C. Kennicutt, Daniela Calzeti, Fabian Walter, George Helou, David J. Hollenbach, Lee Armus, George Bendo, Daniel A. Dale, Bruce T. Draine, Charles W. Engelbracht, Karl D. Gordon, Moire K.M. Prescott, Michael W. Regan, Michele D. Thornley, Caroline Bot, Elias Brinks, Erwin De Blok, Dulia De Mello, Martin Meyer, John MoustakasEric J. Murphy, Kartik Sheth, J. D.T. Smith

Research output: Contribution to journalArticlepeer-review

391 Scopus citations


We have studied the relationship between the star formation rate (SFR), surface density, and gas surface density in the spiral galaxy M51a (NGC 5194), using multiwavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS ). We introduce a new SFR index based on a linear combination of Hα emission-line and 24 μm continuum luminosities, which provides reliable extinction-corrected ionizing fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis H I and CO maps has allowed us to probe the form of the spatially resolved star formation law on scales of 0.5-2 kpc. We find that the resolved SFR versus gas surface density relation is well represented by a Schmidt power law, which is similar in form and dispersion to the disk-averaged Schmidt law. We observe a comparably strong correlation of the SFR surface density with the molecular gas surface density, but no significant correlation with the surface density of atomic gas. The best-fitting slope of the Schmidt law varies from N = 1.37 to 1.56, with zero point and slope that change systematically with the spatial sampling scale. We tentatively attribute these variations to the effects of areal sampling and averaging of a nonlinear intrinsic star formation law. Our data can also be fitted by an alternative parameterization of the SFR surface density in terms of the ratio of gas surface density to local dynamical time, but with a considerable dispersion.

Original languageEnglish (US)
Pages (from-to)333-348
Number of pages16
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: ISM
  • Galaxies: evolution
  • Galaxies: individual (M51a, NGC 5194)
  • H II regions
  • Infrared: galaxies
  • Stars: formation


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