2013A&A...558A..72I

Query : 2013A&A...558A..72I

2013A&A...558A..72I - Astronomy and Astrophysics, volume 558A72-72 (2013/10-1)

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

IACOBELLI M., HAVERKORN M., ORRU E., PIZZO R.F., ANDERSON J., BECK R., BELL M.R., BONAFEDE A., CHYZY K., DETTMAR R.-J., ENSSLIN T.A., HEALD G., HORELLOU C., HORNEFFER A., JURUSIK W., JUNKLEWITZ H., KUNIYOSHI M., MULCAHY D.D., PALADINO R., REICH W., SCAIFE A., SOBEY C., SOTOMAYOR-BELTRAN C., ALEXOV A., ASGEKAR A., AVRUCH I.M., BELL M.E., VAN BEMMEL I., BENTUM M.J., BERNARDI G., BEST P., BIRZAN L., BREITLING F., BRODERICK J., BROUW W.N., BRUEGGEN M., BUTCHER H.R., CIARDI B., CONWAY J.E., DE GASPERIN F., DE GEUS E., DUSCHA S., EISLOEFFEL J., ENGELS D., FALCKE H., FALLOWS R.A., FERRARI C., FRIESWIJK W., GARRETT M.A., GRIESSMEIER J., GUNST A.W., HAMAKER J.P., HASSALL T.E., HESSELS J.W.T., HOEFT M., HOERANDEL J., JELIC V., KARASTERGIOU A., KONDRATIEV V.I., KOOPMANS L.V.E., KRAMER M., KUPER G., VAN LEEUWEN J., MACARIO G., MANN G., McKEAN J.P., MUNK H., PANDEY-POMMIER M., POLATIDIS A.G., ROETTGERING H., SCHWARZ D., SLUMAN J., SMIRNOV O., STAPPERS B.W., STEINMETZ M., TAGGER M., TANG Y., TASSE C., TORIBIO C., VERMEULEN R., VOCKS C., VOGT C., VAN WEEREN R.J., WISE M.W., WUCKNITZ O., YATAWATTA S., ZARKA P. and ZENSUS A.

Abstract (from CDS):

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. 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''x70'' 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. 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 ∼20pc 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. 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.

Abstract Copyright: ∼

Journal keyword(s): ISM: general - ISM: magnetic fields - ISM: structure - radio continuum: general - radio continuum: ISM - techniques: interferometric

Simbad objects: 17

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Number of rows : 17
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 BD-17 83 * 00 35 04.4684908320 -16 25 01.662502620   11.837 11.549     A7 8 0
2 M 33 GiG 01 33 50.8965749232 +30 39 36.630403128 6.17 6.27 5.72     ~ 6226 1
3 SNR G130.7+03.1 SNR 02 05 35.73 +64 49 41.3           ~ 661 4
4 W 3 MoC 02 27 04.10 +61 52 27.1           ~ 1064 3
5 NAME Heart Nebula HII 02 32.7 +61 27           ~ 336 1
6 4C 63.05 Rad 02 35 43.060 +63 22 33.33           ~ 11 1
7 26P 3 Sy1 02 38 02.358 +59 11 50.02           ~ 80 1
8 IC 1848 OpC 02 51 19.4 +60 25 32   6.87 6.5     ~ 522 2
9 [DSL2000] 0313+683 Rad 03 17 51 +68 29.0           ~ 3 0
10 NAME Per Arm PoG 03 30 +45.0           ~ 1672 0
11 IC 342 AGN 03 46 48.514 +68 05 45.98   10.5       ~ 1579 1
12 4C 72.06 Rad 03 54 55.01 +72 54 39.7           ~ 11 1
13 M 51 Sy2 13 29 52.698 +47 11 42.93   9.26 8.36 8.40   ~ 4565 4
14 NAME Sgr Arm PoG 19 00 -30.0           ~ 710 1
15 MCG+07-41-003 Bla 19 59 28.35656837 +40 44 02.0972325   16.22 15.10     ~ 2537 2
16 NGC 6946 H2G 20 34 52.332 +60 09 13.24   10.5       ~ 2661 2
17 NAME Cas A SNR 23 23 26.0 +58 48 41     14.30     ~ 3033 1

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