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Date and Time of the Query: 2019-06-26 T23:04:51 PDT
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For refcode 2012ApJ...750..126M:
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2012ApJ...750..126M Characterizing Cosmic-Ray Propagation in Massive Star-forming Regions: The Case of 30 Doradus and the Large Magellanic Cloud Murphy, E. J.; Porter, T. A.; Moskalenko, I. V.; Helou, G.; Strong, A. W. Abstract. Using infrared, radio, and gamma-ray data, we investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using a phenomenological model based on the radio-far-infrared correlation within galaxies. Employing a correlation analysis, we derive an average propagation length of ~100-140 pc for ~3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed gamma-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and gamma-ray data, we estimate a ~20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for ~3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is ~4 times higher, scaling as (R/GV)^delta^ with delta ~ 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include ~70 GeV CR nuclei traced by the 3-10 GeV gamma-ray data (delta ~ 0.66 +/- 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D_R_ ~ (0.9-1.0) x 10^27^(R/GV)^0.7^ cm^2^ s^-1^. We compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor. Key words: cosmic rays, galaxies: individual: LMC, gamma rays: galaxies, H II regions, infrared: galaxies, radio continuum: galaxies, stars: formation
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