Studying Galactic interstellar turbulence through fluctuations in synchrotron emission: First LOFAR Galactic foreground detection
Abstract
The characteristic outer scale of turbulence and the ratio of the random to ordered components of the magnetic field are key parameters to characterise magnetic turbulence in the interstellar gas, which affects the propagation of cosmic rays within the Galaxy. We provide new constraints to those two parameters. We use the LOw Frequency ARray (LOFAR) to image the diffuse continuum emission in the Fan region at (l,b) (137.0,+7.0) at 80"x70" resolution in the range [146,174] MHz. We detect multi-scale fluctuations in the Galactic synchrotron emission and compute their power spectrum. Applying theoretical estimates and derivations from the literature for the first time, we derive the outer scale of turbulence and the ratio of random to ordered magnetic field from the characteristics of these fluctuations . We obtain the deepest image of the Fan region to date and find diffuse continuum emission within the primary beam. The power spectrum of the foreground synchrotron fluctuations displays a power law behaviour for scales between 100 and 8 arcmin with a slope of (-1.84+/-0.19). We find an upper limit of about 20 pc for the outer scale of the magnetic interstellar turbulence toward the Fan region. We also find a variation of the ratio of random to ordered field as a function of Galactic coordinates, supporting different turbulent regimes. We use power spectra fluctuations from LOFAR as well as earlier GMRT and WSRT observations to constrain the outer scale of turbulence of the Galactic synchrotron foreground, finding a range of plausible values of 10-20 pc. Then, we use this information to deduce lower limits of the ratio of ordered to random magnetic field strength. These are found to be 0.3, 0.3, and 0.5 for the LOFAR, WSRT and GMRT fields considered respectively. Both these constraints are in agreement with previous estimates.
Keywords
Cite
@article{arxiv.1308.2804,
title = {Studying Galactic interstellar turbulence through fluctuations in synchrotron emission: First LOFAR Galactic foreground detection},
author = {M. Iacobelli and M. Haverkorn and E. Orrú and R. F. Pizzo and J. Anderson and R. Beck and M. R. Bell and A. Bonafede and K. Chyzy and R. -J. Dettmar and T. A. Enßlin and G. Heald and C. Horellou and A. Horneffer and W. Jurusik and H. Junklewitz and M. Kuniyoshi and D. D. Mulcahy and R. Paladino and W. Reich and A. Scaife and C. Sobey and C. Sotomayor-Beltran and A. Alexov and A. Asgekar and I. M. Avruch and M. E. Bell and I. van Bemmel and M. J. Bentum and G. Bernardi and P. Best and L. Birzan and F. Breitling and J. Broderick and W. N. Brouw and M. Bruggen and H. R. Butcher and B. Ciardi and J. E. Conway and F. de Gasperin and E. de Geus and S. Duscha and J. Eisloffel and D. Engels and H. Falcke and R. A. Fallows and C. Ferrari and W. Frieswijk and M. A. Garrett and J. Griessmeier and A. W. Gunst and J. P. Hamaker and T. E. Hassall and J. W. T. Hessels and M. Hoeft and J. Horandel and V. Jelic and A. Karastergiou and V. I. Kondratiev and L. V. E. Koopmans and M. Kramer and G. Kuper and J. van Leeuwen and G. Macario and G. Mann and J. P. McKean and H. Munk and M. Pandey-Pommier and A. G. Polatidis and H. Röttgering and D. Schwarz and J. Sluman and O. Smirnov and B. W. Stappers and M. Steinmetz and M. Tagger and Y. Tang and C. Tasse and C. Toribio and R. Vermeulen and C. Vocks and C. Vogt and R. J. van Weeren and M. W. Wise and O. Wucknitz and S. Yatawatta and P. Zarka and A. Zensus},
journal= {arXiv preprint arXiv:1308.2804},
year = {2013}
}
Comments
13 pages, 11 figures, accepted for publication in A&A