Studying Galactic interstellar turbulence through fluctuations in synchrotron emission: First LOFAR Galactic foreground detection
Journal article, 2013
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. © 2013 ESO.
Techniques: interferometric
ISM: magnetic fields
Radio continuum: general
ISM: structure
ISM: general
Radio continuum: ISM
Author
M. Iacobelli
Netherlands Institute for Radio Astronomy (ASTRON)
Leiden University
M. Haverkorn
Leiden University
Radboud University
E. Orru
Radboud University
Netherlands Institute for Radio Astronomy (ASTRON)
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
J. Anderson
Max Planck Society
R. Beck
Max Planck Society
M. R. Bell
Max Planck Society
A. Bonafede
University of Hamburg
K.T. Chyz̊y
Jagiellonian University in Kraków
R.J. Dettmar
Ruhr-Universität Bochum
T.A. Enßlin
Max Planck Society
G. Heald
Netherlands Institute for Radio Astronomy (ASTRON)
Cathy Horellou
Astronomy and Plasmaphysics
A. Horneffer
Max Planck Society
W. Jurusik
Jagiellonian University in Kraków
H. Junklewitz
Max Planck Society
M. Kuniyoshi
Max Planck Society
D.D. Mulcahy
Max Planck Society
R. Paladino
University of Bologna
W. Reich
Max Planck Society
A. Scaife
University of Southampton
C. Sobey
Max Planck Society
C. Sotomayor-Beltran
Ruhr-Universität Bochum
A. Alexov
Space Telescope Science Institute (STScI)
A. Asgekar
Netherlands Institute for Radio Astronomy (ASTRON)
I.M. Avruch
Netherlands Institute for Space Research (SRON)
M.E. Bell
The University of Sydney
I. van Bemmel
Netherlands Institute for Radio Astronomy (ASTRON)
M.J. Bentum
Netherlands Institute for Radio Astronomy (ASTRON)
G.C. Bernardi
Harvard-Smithsonian Center for Astrophysics
P.N. Best
University of Edinburgh
L. Birzan
Leiden University
F. Breitling
Leibniz Institute for Astrophysics Potsdam
J.W. Broderick
University of Southampton
W.N. Brouw
University of Groningen
M. Brüggen
University of Hamburg
H.R. Butcher
Australian National University
B. Ciardi
Max Planck Society
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
F. De Gasperin
University of Hamburg
E.J. De Geus
Netherlands Institute for Radio Astronomy (ASTRON)
S. Duscha
Netherlands Institute for Radio Astronomy (ASTRON)
J. Eislöffel
D. Engels
University of Hamburg
H.D. Falcke
Netherlands Institute for Radio Astronomy (ASTRON)
Radboud University
R.A. Fallows
Netherlands Institute for Radio Astronomy (ASTRON)
C. Ferrari
Université Nice Sophia Antipolis (UNS)
W. Frieswijk
Netherlands Institute for Radio Astronomy (ASTRON)
M.A. Garrett
Leiden University
Netherlands Institute for Radio Astronomy (ASTRON)
J.M. Grießmeier
Centre national de la recherche scientifique (CNRS)
A.W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
J.P. Hamaker
Netherlands Institute for Radio Astronomy (ASTRON)
T.E. Hassall
University of Southampton
University of Manchester
J.W.T. Hessels
Netherlands Institute for Radio Astronomy (ASTRON)
Anton Pannekoek Institute for Astronomy
M. Hoeft
J.R. Hörandel
Radboud University
V. Jelić
Netherlands Institute for Radio Astronomy (ASTRON)
A. Karastergiou
University of Oxford
V.I. Kondratiev
Russian Academy of Sciences
Netherlands Institute for Radio Astronomy (ASTRON)
L.V.E. Koopmans
University of Groningen
M.A. Kramer
Max Planck Society
G. Kuper
Netherlands Institute for Radio Astronomy (ASTRON)
J. van Leeuwen
Netherlands Institute for Radio Astronomy (ASTRON)
G. Macario
Université Nice Sophia Antipolis (UNS)
G. Mann
Leibniz Institute for Astrophysics Potsdam
J. McKean
Netherlands Institute for Radio Astronomy (ASTRON)
H. Munk
Netherlands Institute for Radio Astronomy (ASTRON)
M. Pandey-Pommier
Lyon Observatory
A.G. Polatidis
Netherlands Institute for Radio Astronomy (ASTRON)
H. Rottgering
Leiden University
D.J. Schwarz
Bielefeld University
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
O. M. Smirnov
Rhodes University
B.W. Stappers
University of Manchester
M. Steinmetz
Leibniz Institute for Astrophysics Potsdam
M. Tagger
Centre national de la recherche scientifique (CNRS)
Y. Tang
Netherlands Institute for Radio Astronomy (ASTRON)
C. Tasse
Observatoire de Paris-Meudon
C. Toribio
Netherlands Institute for Radio Astronomy (ASTRON)
R.C. Vermeulen
Netherlands Institute for Radio Astronomy (ASTRON)
C. Vocks
Leibniz Institute for Astrophysics Potsdam
C. Vogt
Netherlands Institute for Radio Astronomy (ASTRON)
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
M.W. Wise
Netherlands Institute for Radio Astronomy (ASTRON)
Anton Pannekoek Institute for Astronomy
O. Wucknitz
Max Planck Society
University of Bonn
S.B. Yatawatta
Netherlands Institute for Radio Astronomy (ASTRON)
P.M. Zarka
Observatoire de Paris-Meudon
A.J. Zensus
Max Planck Society
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 558 721- A72Subject Categories
Physical Sciences
Roots
Basic sciences
Infrastructure
Onsala Space Observatory
DOI
10.1051/0004-6361/201322013