Studying Galactic interstellar turbulence through fluctuations in synchrotron emission: First LOFAR Galactic foreground detection
Artikel i vetenskaplig tidskrift, 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.
ISM: structure
Radio continuum: ISM
Techniques: interferometric
ISM: general
Radio continuum: general
ISM: magnetic fields
Författare
M. Iacobelli
Netherlands Institute for Radio Astronomy (ASTRON)
Universiteit Leiden
M. Haverkorn
Radboud Universiteit
Universiteit Leiden
E. Orru
Radboud Universiteit
Netherlands Institute for Radio Astronomy (ASTRON)
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
J. Anderson
Max-Planck-Gesellschaft
R. Beck
Max-Planck-Gesellschaft
M. R. Bell
Max-Planck-Gesellschaft
A. Bonafede
Universität Hamburg
K.T. Chyz̊y
Uniwersytet Jagiellonski w Krakowie
R.J. Dettmar
Ruhr-Universität Bochum
T.A. Enßlin
Max-Planck-Gesellschaft
G. Heald
Netherlands Institute for Radio Astronomy (ASTRON)
Cathy Horellou
Astronomi och plasmafysik
A. Horneffer
Max-Planck-Gesellschaft
W. Jurusik
Uniwersytet Jagiellonski w Krakowie
H. Junklewitz
Max-Planck-Gesellschaft
M. Kuniyoshi
Max-Planck-Gesellschaft
D.D. Mulcahy
Max-Planck-Gesellschaft
R. Paladino
Universita di Bologna
W. Reich
Max-Planck-Gesellschaft
A. Scaife
University of Southampton
C. Sobey
Max-Planck-Gesellschaft
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
Universiteit Leiden
F. Breitling
Leibniz-Gemeinschaft
J.W. Broderick
University of Southampton
W.N. Brouw
Rijksuniversiteit Groningen
M. Brüggen
Universität Hamburg
H.R. Butcher
Australian National University
B. Ciardi
Max-Planck-Gesellschaft
John Conway
Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium
F. De Gasperin
Universität Hamburg
E.J. De Geus
Netherlands Institute for Radio Astronomy (ASTRON)
S. Duscha
Netherlands Institute for Radio Astronomy (ASTRON)
J. Eislöffel
D. Engels
Universität Hamburg
H.D. Falcke
Netherlands Institute for Radio Astronomy (ASTRON)
Radboud Universiteit
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
Netherlands Institute for Radio Astronomy (ASTRON)
Universiteit Leiden
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 Manchester
University of Southampton
J.W.T. Hessels
Anton Pannekoek Institute for Astronomy
Netherlands Institute for Radio Astronomy (ASTRON)
M. Hoeft
J.R. Hörandel
Radboud Universiteit
V. Jelić
Netherlands Institute for Radio Astronomy (ASTRON)
A. Karastergiou
University of Oxford
V.I. Kondratiev
Netherlands Institute for Radio Astronomy (ASTRON)
Russian Academy of Sciences
L.V.E. Koopmans
Rijksuniversiteit Groningen
M.A. Kramer
Max-Planck-Gesellschaft
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-Gemeinschaft
J. McKean
Netherlands Institute for Radio Astronomy (ASTRON)
H. Munk
Netherlands Institute for Radio Astronomy (ASTRON)
M. Pandey-Pommier
Observatoire de Lyon
A.G. Polatidis
Netherlands Institute for Radio Astronomy (ASTRON)
H. Rottgering
Universiteit Leiden
D.J. Schwarz
Universität Bielefeld
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
O. M. Smirnov
Rhodes University
B.W. Stappers
University of Manchester
M. Steinmetz
Leibniz-Gemeinschaft
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-Gemeinschaft
C. Vogt
Netherlands Institute for Radio Astronomy (ASTRON)
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
M.W. Wise
Anton Pannekoek Institute for Astronomy
Netherlands Institute for Radio Astronomy (ASTRON)
O. Wucknitz
Universität Bonn
Max-Planck-Gesellschaft
S.B. Yatawatta
Netherlands Institute for Radio Astronomy (ASTRON)
P.M. Zarka
Observatoire de Paris-Meudon
A.J. Zensus
Max-Planck-Gesellschaft
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 558 721- A72Ämneskategorier (SSIF 2011)
Fysik
Fundament
Grundläggande vetenskaper
Infrastruktur
Onsala rymdobservatorium
DOI
10.1051/0004-6361/201322013