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Journal Articles Astronomy and Astrophysics - A&A Year : 2013

Studying Galactic interstellar turbulence through fluctuations in synchrotron emission

M. Iacobelli (1, 2) , M. Haverkorn (3, 1) , E. Orrú (2, 3) , R. F. Pizzo (2) , J. Anderson (4) , R. Beck (4) , M. R. Bell (5) , A. Bonafede (6) , K. Chyzy (7) , R.-J. Dettmar (8) , T. A. Ensslin (5) , G. Heald (2) , C. Horellou (5) , A. Horneffer (5) , W. Jurusik (7) , H. Junklewitz (5) , M. Kuniyoshi (4) , D. D. Mulcahy (4) , R. Paladino (9) , W. Reich (4) , A. Scaife (10) , C. Sobey (4) , C. Sotomayor-Beltran (8) , A. Alexov (2) , M. E. Bell (11) , A. Asgekar (2) , I. M. Avruch (12) , I. van Bemmel (2) , M. J. Bentum (2) , G. Bernardi (13) , P. Best (14) , L. Birzan (1) , F. Breitling (15) , J. Broderick (10) , W. N. Brouw (16) , M. Brüggen (6) , H. R. Butcher (2) , B. Ciardi (5) , J. E. Conway (17) , F. de Gasperin (14) , E. de Geus (18) , S. Duscha (2) , J. Eislöffel (19) , D. Engels (20) , H. Falcke (2, 4) , R. A. Fallows (2) , C. Ferrari (21) , W. Frieswijk (2) , M. A. Garrett (2, 1) , Jean-Mathias Griessmeier (22) , A. W. Gunst (2) , J. P. Hamaker (2) , T. E. Hassall (23) , J. W. T. Hessels (24) , M. Hoeft (19) , J. Hörandel (3) , V. Jelic (2) , A. Karastergiou (25) , V. I. Kondratiev (2) , L. V. E. Koopmans (26) , M. Kramer (4) , G. Kuper (2) , J. van Leeuwen (24) , G. Macario (27) , G. Mann (15) , J. P. Mckean (2) , H. Munk (2) , M. Pandey-Pommier (28) , A. G. Polatidis (2) , H. Röttgering (1) , D. Schwarz (29) , J. Sluman (2) , O. Smirnov (30) , B. W. Stappers (23) , M. Steinmetz (15) , Michel Tagger (22) , Y. Tang (2) , C. Tasse (30, 31, 32) , C. Toribio (2) , R. Vermeulen (2) , C. Vocks (15) , C. Vogt (2) , R. J. van Weeren (13, 2) , M. W. Wise (33, 2) , O. Wucknitz (34) , S. Yatawatta (16) , P. Zarka (35, 32) , A. Zensus (5)
1 Leiden Observatory [Leiden]
2 ASTRON - Netherlands Institute for Radio Astronomy
3 Radboud University [Nijmegen]
4 MPIFR - Max-Planck-Institut für Radioastronomie
5 Max Planck Institute for Astrophysics
6 Jacobs University = Constructor University [Bremen]
7 UJ - Uniwersytet Jagielloński w Krakowie = Jagiellonian University
8 Astronomisches Institut der Ruhr-Universität Bochum
9 UNIBO - Alma Mater Studiorum Università di Bologna = University of Bologna
10 School of Physics and Astronomy [Southampton]
11 SIfA - Sydney Institute for Astronomy
12 SRON - SRON Netherlands Institute for Space Research
13 CfA - Harvard-Smithsonian Center for Astrophysics
14 Edin. - University of Edinburgh
15 AIP - Leibniz-Institut für Astrophysik Potsdam
16 Kapteyn Astronomical Institute [Groningen]
17 OSO - Onsala Space Observatory
18 Medstar Research Institute
19 TLS - Thüringer Landessternwarte Tautenburg
20 Hamburger Sternwarte/Hamburg Observatory
21 LAGRANGE - Joseph Louis LAGRANGE
22 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
23 Jodrell Bank Centre for Astrophysics
24 UvA - University of Amsterdam [Amsterdam] = Universiteit van Amsterdam
25 Oxford Astrophysics
26 University of Groningen [Groningen]
27 UNSA - Université de Nice Sophia-Antipolis
28 CRAL - Centre de Recherche Astrophysique de Lyon
29 Universität Bielefeld
30 Rhodes University, Grahamstown
31 SKA South Africa
32 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
33 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
34 AlfA - Argelander-Institut für Astronomie
35 OP - Observatoire de Paris - Site de Paris
C. Horellou
H. Junklewitz
P. Best
  • Function : Author
F. de Gasperin
J. Eislöffel
C. Ferrari
G. Mann
H. Röttgering

Abstract

Aims: The characteristic outer scale of turbulence (i.e. the scale at which the dominant source of turbulence injects energy to the interstellar medium) 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. Methods: 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' × 70' 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. Results: We obtain the deepest image of the Fan region to date and find diffuse continuum emission within the primary beam. The power spectrum displays a power law behaviour for scales between 100 and 8 arcmin with a slope α = -1.84 ± 0.19. We find an upper limit of ~20 pc for the outer scale of the magnetic interstellar turbulence toward the Fan region, which is in agreement with previous estimates in literature. We also find a variation of the ratio of random to ordered field as a function of Galactic coordinates, supporting different turbulent regimes. Conclusions. We present the first LOFAR detection and imaging of the Galactic diffuse synchrotron emission around 160 MHz from the highly polarized Fan region. The power spectrum of the foreground synchrotron fluctuations is approximately a power law with a slope α ≈ -1.84 up to angular multipoles of ≤1300, corresponding to an angular scale of ~8 arcmin. We use power spectra fluctuations from LOFAR as well as earlier GMRT and WSRT observations to constrain the outer scale of turbulence (Lout) 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.
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Dates and versions

insu-01288769 , version 1 (06-07-2017)

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M. Iacobelli, M. Haverkorn, E. Orrú, R. F. Pizzo, J. Anderson, et al.. Studying Galactic interstellar turbulence through fluctuations in synchrotron emission. Astronomy and Astrophysics - A&A, 2013, 558, pp.A72. ⟨10.1051/0004-6361/201322013⟩. ⟨insu-01288769⟩
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