An absolutely calibrated survey of polarized   emission from the northern sky at 1.4 GHz

Wolleben, M.; Landecker, T. L.; Reich, W.; Wielebinski, R.

doi:10.1051/0004-6361:20053851

Cited by 185 publications

(284 citation statements)

References 22 publications

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“…Actually, the complete high-polarisation Fan region stretches out over (l, b) ≈ (90 • −190 • , −5 • −25 • ) and therefore also encompasses the Ghosh field. Indeed, Wolleben et al (2006) argue from depolarisation arguments that the Fan region has to extend (Bernardi et al 2009), and GMRT (Ghosh et al 2012) estimates of the outer scale of turbulence of the Galaxy towards the second Galactic quadrant with earlier observations from Ohno & Shibata (1993), Clegg et al (1992), Haverkorn et al (2008), Malkov et al (2010), and. The turbulence scale derived by Fletcher et al (2011) and Beck et al (1999) for the nearby spiral galaxies M 51 and NGC 6946 respectively are also shown.…”

Section: Discussionsupporting

confidence: 57%

Studying Galactic interstellar turbulence through fluctuations in synchrotron emission

Iacobelli

Haverkorn

Orrù

et al. 2013

A&A

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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 (L out ) 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.

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Section: Discussionsupporting

confidence: 57%

Studying Galactic interstellar turbulence through fluctuations in synchrotron emission

Iacobelli

Haverkorn

Orrù

et al. 2013

A&A

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“…Wolleben (2007) modelled the NPS as two local shells based mainly on DRAO 1.4 GHz all-sky polarization survey data (Wolleben et al 2006). However, this polarization survey suffers strong depolarization for latitudes below about 30 • , which prevents the tracking of the NPS towards low latitudes.…”

Section: The Southern North Polar Spur Extensionmentioning

confidence: 99%

A Sino-Germanλ6 cm polarization survey of the Galactic plane

Sun

Reich

Han

et al. 2011

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Aims. We study polarized short-wavelength emission from the inner Galaxy, which is nearly invisible at long wavelengths because of depolarization. We attempt to obtain information on the diffuse continuum emission at short wavelengths to help us to separate Galactic thermal and non-thermal components. Methods. We conducted a total intensity and polarization survey of the Galactic plane at λ6 cm using the Urumqi 25 m telescope for the Galactic longitude range of 10 • ≤ l ≤ 60 • and the Galactic latitude range of |b| ≤ 5 • . Missing absolute zero levels of Stokes U and Q maps were restored by extrapolating the WMAP five-year K-band polarization data. For total intensities, we recovered missing large-scale components by referring to the Effelsberg λ11 cm survey. Results. Total intensity and polarization maps are presented with an angular resolution of 9. 5 and a sensitivity of 1 mK T B and 0.5 mK T B in total and polarized intensity, respectively. The λ6 cm polarized emission in the Galactic plane originates within about 4 kpc distance, which increases for polarized emission out of the plane. The polarization map shows "patches", "canals", and "voids" with no correspondence in total intensity. We attribute the patches to turbulent magnetic field cells. Canals are caused by abrupt variation in the polarization angles at the boundaries of patches rather than by foreground Faraday screens. The superimposition of foreground and Faraday screen rotated background emission almost cancels the polarized emission locally, such that polarization voids appear. By modelling the voids, we estimate the Faraday screen's regular magnetic field along the line-of-sight to be larger than about 8 μG. We separated thermal (free-free) and non-thermal (synchrotron) emission according to their different spectral indices. The spectral index for the synchrotron emission is based on WMAP polarization data. The fraction of thermal emission at λ6 cm is about 60% in the plane. Conclusions. The Sino-German λ6 cm polarization survey of the inner Galaxy provides new insights into the properties of the magnetized interstellar medium for this very complex Galactic region, which is Faraday thin up to about 4 kpc in the Galactic plane. Within this distance polarized patches are identified as intrinsic structures related to turbulent Galactic magnetic fields of spatial scales from 20(d/4 kpc) to 200(d/4 kpc) pc.

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“…Also it will be crucial to analyse microwave data together with ancillary data from radio and infrared frequencies. 4 During the final phase of the revision process of this work, the DRAO 1.4 GHz polarization survey has been released (Wolleben et al 2006). The data are available at http://www.mpifr-bonn.mpg.de/div/konti/26msurvey/ or http://www.drao-ofr.hia-iha.nrc-cnrc.gc.ca/26msurvey/ or http://cdsweb.u-strasbg.fr/cgi-bin/qcat/?J/A+A/448/411.…”

Section: Introductionmentioning

confidence: 99%

A multifrequency angular power spectrum analysis of the Leiden polarization surveys

Porta

Burigana

2006

A&A

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The Galactic synchrotron emission is expected to be the most relevant source of astrophysical contamination in cosmic microwave background polarization measurements, at least at frequencies ν < ∼ 70 GHz and at angular scales θ > ∼ 30 . We present a multifrequency analysis of the Leiden surveys, linear polarization surveys covering the Northern Celestial Hemisphere at five frequencies between 408 MHz and 1411 MHz. By implementing specific interpolation methods to deal with these irregularly sampled data, we produced maps of the polarized diffuse Galactic radio emission with a pixel size 0.92 • . We derived the angular power spectrum (APS) (PI, E, and B modes) of the synchrotron dominated radio emission as function of the multipole, . We considered the whole covered region and some patches at different Galactic latitudes. By fitting the APS in terms of power laws (C ∼ κ · α ), we found spectral indices that steepen with increasing frequency: from α ∼ −(1−1.5) at 408 MHz to α ∼ −(2−3) at 1411 MHz for 10 < ∼ < ∼ 100 and from α ∼ −0.7 to α ∼ −1.5 for lower multipoles (the exact values depending on the considered sky region and polarization mode). The bulk of this flattening at lower frequencies can be interpreted in terms of Faraday depolarization effects. We then considered the APS at various fixed multipoles and its frequency dependence. Using the APSs of the Leiden surveys at 820 MHz and 1411 MHz, we determined possible ranges for the rotation measure, RM, in the simple case of an interstellar medium slab model. Also taking into account the polarization degree at 1.4 GHz, it is possible to break the degeneracy between the identified RM intervals. The most reasonable of them turned out to be RM ∼ 9−17 rad/m 2 although, given the uncertainty on the measured polarization degree, RM values in the interval ∼53−59 rad/m 2 cannot be excluded.

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An absolutely calibrated survey of polarized emission from the northern sky at 1.4 GHz

Cited by 185 publications

References 22 publications

Studying Galactic interstellar turbulence through fluctuations in synchrotron emission

Studying Galactic interstellar turbulence through fluctuations in synchrotron emission

A Sino-Germanλ6 cm polarization survey of the Galactic plane

A multifrequency angular power spectrum analysis of the Leiden polarization surveys

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