Studying Galactic interstellar turbulence through fluctuations in synchrotron emission First LOFAR Galactic foreground detection

被引：83

作者：

Iacobelli, M. ^{[1
,2
]}

Haverkorn, M. ^{[1
,3
]}

Orru, E. ^{[2
,3
]}

Pizzo, R. F. ^{[2
]}

Anderson, J. ^{[4
]}

Beck, R. ^{[4
]}

Bell, M. R. ^{[5
]}

Bonafede, A. ^{[6
]}

Chyzy, K. ^{[7
]}

Dettmar, R. -J. ^{[8
]}

Ensslin, T. A. ^{[9
]}

Heald, G. ^{[2
]}

Horellou, C. ^{[10
]}

Horneffer, A. ^{[4
]}

Jurusik, W. ^{[7
]}

Junklewitz, H. ^{[9
]}

Kuniyoshi, M. ^{[4
]}

Mulcahy, D. D. ^{[4
]}

Paladino, R. ^{[34
]}

Reich, W. ^{[4
]}

Scaife, A. ^{[11
]}

Sobey, C. ^{[4
]}

Sotomayor-Beltran, C. ^{[8
]}

Alexov, A. ^{[12
]}

Asgekar, A. ^{[2
]}

Avruch, I. M. ^{[13
]}

Bell, M. E. ^{[14
]}

van Bemmel, I. ^{[2
]}

Bentum, M. J. ^{[2
]}

Bernardi, G. ^{[15
]}

Best, P. ^{[16
]}

Birzan, L. ^{[1
]}

Breitling, F. ^{[17
]}

Broderick, J. ^{[11
]}

Brouw, W. N. ^{[18
]}

Brueggen, M. ^{[6
]}

Butcher, H. R. ^{[19
]}

Ciardi, B. ^{[5
]}

Conway, J. E. ^{[10
]}

de Gasperin, F. ^{[6
]}

de Geus, E. ^{[2
]}

Duscha, S. ^{[2
]}

Eisloeffel, J. ^{[20
]}

Engels, D. ^{[21
]}

Falcke, H. ^{[31
]}

Fallows, R. A. ^{[2
]}

Ferrari, C. ^{[22
]}

Frieswijk, W. ^{[2
]}

Garrett, M. A. ^{[20
]}

Griessmeier, J. ^{[23
]}

机构：

[1] Leiden Univ, Leiden Observ, NL-2300 RA Leiden, Netherlands

[2] Netherlands Inst Radio Astron ASTRON, NL-7990 AA Dwingeloo, Netherlands

[3] Radboud Univ Nijmegen, NL-6525 AJ Nijmegen, Netherlands

[4] Max Planck Inst Radioastron, D-53121 Bonn, Germany

[5] Max Planck Inst Astrophys, D-85741 Garching, Germany

[6] Univ Hamburg, D-21029 Hamburg, Germany

[7] Jagiellonian Univ, PL-30244 Krakow, Poland

[8] Ruhr Univ Bochum, Astron Inst, D-44780 Bochum, Germany

[9] Max Planck Inst Astrophys, D-85748 Garching, Germany

[10] Chalmers Univ Technol, Onsala Space Observ, Dept Earth & Space Sci, S-43992 Onsala, Sweden

[11] Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England

[12] Space Telescope Sci Inst, Baltimore, MD 21218 USA

[13] SRON Netherlands Insitute Space Res, NL-9700 AV Groningen, Netherlands

[14] Univ Sydney, Sydney Inst Astron, ARC Ctr Excellence All Sky Astrophys CAASTRO, Sydney, NSW 2006, Australia

[15] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA

[16] Univ Edinburgh, Royal Observ Edinburgh, Inst Astron, Edinburgh EH9 3HJ, Midlothian, Scotland

[17] Leibniz Inst Astrophys Potsdam AIP, D-14482 Potsdam, Germany

[18] Univ Groningen, Kapteyn Astron Inst, NL-9700 AV Groningen, Netherlands

[19] Australian Natl Univ, Res Sch Astron & Astrophys, Mt Stromlo Obs, Weston, ACT 2611, Australia

[20] Thuringer Landessternwarte, D-07778 Tautenburg, Germany

[21] Hamburger Sternwarte, D-21029 Hamburg, Germany

[22] Univ Nice Sophia Antipolis, CNRS, Observ Cote Azur, Lab Lagrange,UMR7293, F-06300 Nice, France

[23] CNRS, UMR 7328, LPC2E, F-45071 Orleans 02, France

[24] Univ Oxford, Oxford OX1 3RH, England

[25] Observ Lyon, Ctr Rech Astrophys Lyon, F-69561 St Genis Laval, France

[26] Univ Bielefeld, Fak Phys, D-33501 Bielefeld, Germany

[27] Rhodes Univ, Dept Phys & Elect, Ctr Radio Astron Tech & Technol RATT, ZA-6140 Grahamstown, South Africa

[28] Univ Manchester, Sch Phys & Astron, Jodrell Bank Ctr Astrophys, Manchester M13 9PL, Lancs, England

[29] Observ Paris, CNRS, UMR 8109, LESIA, F-92195 Meudon, France

[30] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1090 GE Amsterdam, Netherlands

[31] PN Lebedev Phys Inst, Ctr Astro Space, Moscow 117997, Russia

[32] SKA South Africa, ZA-7405 Pinelands, South Africa

[33] Univ Bonn, Argelander Inst Astron, D-53121 Bonn, Germany

[34] Univ Bologna, INAF ALMA Reg Ctr, I-40129 Bologna, Italy

来源：

ASTRONOMY & ASTROPHYSICS | 2013年 / 558卷

关键词：

ISM: general; ISM: magnetic fields; ISM: structure; radio continuum: general; radio continuum: ISM techniques; interferometric; ANGULAR POWER SPECTRUM; MAGNETIC-FIELD; RADIO-EMISSION; W-PROJECTION; WIDE-FIELD; POLARIZATION; MHZ; POLARIMETRY; ANISOTROPY; REGION;

D O I：

10.1051/0004-6361/201322013

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

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 '' x 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 a = -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 a beta-1.84 up to angular multipoles of similar to 1300, corresponding to an angular scale of similar to 8 arcmin. We use power spectra fluctuations from LOFAR as well as earlier GMRT andWSRT 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.

引用

页数：13

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