Characterizing Cosmic-Ray Propagation in Massive Star-forming Regions: The Case of 30 Doradus and the Large Magellanic Cloud

Creators: Murphy, E. J.; Porter, T. A.; Moskalenko, I. V.; Helou, G.; Strong, A. W.

Abstract

Using infrared, radio, and γ-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 γ-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and γ-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)δ with δ ≈ 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 γ-ray data (δ ≈ 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) × 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.

Additional Information

© 2012 American Astronomical Society. Received 2012 January 24; accepted 2012 March 7; published 2012 April 24. We thank the anonymous referee for useful suggestions that helped to improve the content and presentation of this paper. E. J. M. thanks Annie Hughes for both providing us with radio maps and for useful discussions which greatly helped shape the paper. We are grateful to the SAGE team for producing high quality data sets used in this study. T.A.P. and E.J.M. acknowledge support via NASA grant NNX10AE78G. I.V.M. acknowledges support via NASA grant NNX09AC15G. The Fermi-LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d' Études Spatiales in France. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This research has additionally made use of the NASA/IPAC Extragalactic Database (NED), which is also operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

Attached Files

Published - Murphy2012p18284Astrophys_J.pdf

Files

Murphy2012p18284Astrophys_J.pdf

Files (798.7 kB)

Name	Size	Download all
Murphy2012p18284Astrophys_J.pdf md5:1a160fae72d238656c1a143f544fea77	798.7 kB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes