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.

ISM: magnetic fields

Radio continuum: ISM

Radio continuum: general

ISM: structure

Techniques: interferometric

ISM: general

Author

M. Iacobelli

Leiden University

Netherlands Institute for Radio Astronomy (ASTRON)

M. Haverkorn

Radboud University

Leiden University

E. Orru

Radboud University

Netherlands Institute for Radio Astronomy (ASTRON)

R. Pizzo

Netherlands Institute for Radio Astronomy (ASTRON)

J. Anderson

Max Planck Institute

R. Beck

Max Planck Institute

M. R. Bell

Max Planck Institute

A. Bonafede

Universität Hamburg

K.T. Chyz̊y

Jagiellonian University in Kraków

R.J. Dettmar

Ruhr-Universität Bochum

T.A. Enßlin

Max Planck Institute

G. Heald

Netherlands Institute for Radio Astronomy (ASTRON)

Cathy Horellou

Astronomy and Plasmaphysics

A. Horneffer

Max Planck Institute

W. Jurusik

Jagiellonian University in Kraków

H. Junklewitz

Max Planck Institute

M. Kuniyoshi

Max Planck Institute

D.D. Mulcahy

Max Planck Institute

R. Paladino

University of Bologna

W. Reich

Max Planck Institute

A. Scaife

University of Southampton

C. Sobey

Max Planck Institute

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

Astrophysikalisches Institut Potsdam

J.W. Broderick

University of Southampton

W.N. Brouw

University of Groningen

M. Brüggen

Universität Hamburg

H.R. Butcher

Australian National University

B. Ciardi

Max Planck Institute

John Conway

Chalmers, Earth and Space Sciences, Onsala Space Observatory

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 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

Anton Pannekoek Institute for Astronomy

Netherlands Institute for Radio Astronomy (ASTRON)

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 Institute

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

Astrophysikalisches Institut Potsdam

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

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

Astrophysikalisches Institut Potsdam

M. Tagger

Centre national de la recherche scientifique (CNRS)

Y. Tang

Netherlands Institute for Radio Astronomy (ASTRON)

C. Tasse

GEPI - Galaxies, Etoiles, Physique, Instrumentation

C. Toribio

Netherlands Institute for Radio Astronomy (ASTRON)

R.C. Vermeulen

Netherlands Institute for Radio Astronomy (ASTRON)

C. Vocks

Astrophysikalisches Institut 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 Institute

University of Bonn

S.B. Yatawatta

Netherlands Institute for Radio Astronomy (ASTRON)

P.M. Zarka

GEPI - Galaxies, Etoiles, Physique, Instrumentation

A.J. Zensus

Max Planck Institute

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 558 721- A72

Subject Categories

Physical Sciences

Roots

Basic sciences

Infrastructure

Onsala Space Observatory

DOI

10.1051/0004-6361/201322013

More information

Latest update

12/11/2018