On Large-Scale Magnetic Field Reversals in the Outer Galaxy

Brown, J. C.; Taylor, A. R.; Wielebinski, R.; Mueller, P.

doi:10.1086/377365

Cited by 50 publications

(52 citation statements)

References 22 publications

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“…In their modeling, Brown et al (2007) assumed that the strength of the large-scale field decreases with Galactocentric radius, following results by Heiles (1996), Beck (2001), and Brown et al (2003). However, we do not find strong evidence for a systematic variation with galactocentric radius of the strength of the large-scale field.…”

Section: Summary and Discussionsupporting

confidence: 83%

The large-scale magnetic field in the fourth Galactic quadrant

Nota¹,

Katgert²

2010

A&A

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Aims. We have re-examined the published rotation measures (RMs) of extragalactic point sources and pulsars with |b| < 3 • to study the magnetic field in the fourth Galactic quadrant. Methods. We reduced the influence of structure in electron density as much as possible by excluding objects for which Hα-data indicate large fluctuations in n e somewhere along the line of sight. We also excluded objects for which the RM may have been significantly "corrupted" by an intervening supernova remnant. We modeled RM(l), the longitude dependence of RM of the unaffected extragalactic sources and pulsars. We assumed several geometries for the large-scale field. All but one of those are based on logarithmic spiral arms (with various pitch angles and widths), while one has circular symmetry. We also made different assumptions about the large-scale n e -distribution. Results. The data suggest the following generic behaviour of the large-scale field in the 4th Galactic quadrant. The field is most likely organized along logarithmic spiral arms and shows two significant reversals: from the Norma arm (CCW field) to the Norma-Crux interarm region (CW field), and from the Norma-Crux interarm region to the Crux arm (CCW field). The present data do not constrain the field in and beyond the Crux-Carina interarm region. Although the models give a good description of the global character of RM(l), individual RM-estimates deviate by typically 15 times their measurement errors. We argue that these large deviations are most likely due to the "small-scale" field that dominates on scales of up to several hundred pc. Conclusions. The picture that emerges is thus of a field that has significant structure on smaller scales, but for which the average values in arms and interarm regions are nevertheless well-defined. In addition, this smaller-amplitude large-scale field appears to reverse at each arm-interarm boundary that we can study with the present data. We briefly discuss the link between these results and theoretical predictions.

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Section: Summary and Discussionsupporting

confidence: 83%

The large-scale magnetic field in the fourth Galactic quadrant

Nota¹,

Katgert²

2010

A&A

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“…The region boundaries are delineated by the green spirals in Figure 4. The constraints for the model field within each arm or interarm region are (1) a logspiral with a pitch angle of 11.5 as shown, (2) a field strength that is inversely proportional to Galactic radius (e.g., Heiles 1996b; Beck 2001;Brown et al 2003b), (3) a zero vertical component, and (4) a coherent direction within each region. We set the magnetic field within the molecular ring to have the same constraints as in the arms, except that the field is assumed to be purely azimuthal.…”

Section: Modeling the Large-scale Magnetic Fieldmentioning

confidence: 99%

Rotation Measures of Extragalactic Sources behind the Southern Galactic Plane: New Insights into the Large‐Scale Magnetic Field of the Inner Milky Way

Brown

Haverkorn

Gaensler

et al. 2007

ApJ

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225

287

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We present new Faraday rotation measures ( RMs) for 148 extragalactic radio sources behind the southern Galactic plane (253 l 356 , jbj 1:5 ), and use these data in combination with published data to probe the large-scale structure of the Milky Way's magnetic field. We show that the magnitudes of these RMs oscillate with longitude in a manner that correlates with the locations of the Galactic spiral arms. The observed pattern in RMs requires the presence of at least one large-scale magnetic reversal in the fourth Galactic quadrant, located between the SagittariusCarina and Scutum-Crux spiral arms. To quantitatively compare our measurements to other recent studies, we consider all available extragalactic and pulsar RMs in the region we have surveyed, and jointly fit these data to simple models in which the large-scale field follows the spiral arms. In the best-fitting model, the magnetic field in the fourth Galactic quadrant is directed clockwise in the Sagittarius-Carina spiral arm (as viewed from the north Galactic pole), but is oriented counterclockwise in the Scutum-Crux arm. This contrasts with recent analyses of pulsar RMs alone, in which the fourth-quadrant field was presumed to be directed counterclockwise in the Sagittarius-Carina arm. Also in contrast to recent pulsar RM studies, our joint modeling of pulsar and extragalactic RMs demonstrates that large numbers of large-scale magnetic field reversals are not required to account for observations.

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“…If the blob is a Perseus arm object like W5, a positive RM FS is preferred, because of the larger c value. Brown et al (2003b) examined the RM values of extragalactic sources and pulsars in the direction of 105 • ≤ ≤ 135 • within the Galactic plane and found that most values are negative. However, Mitra et al (2003) showed a schematic model (their Fig.…”

Section: W5 ( = 137mentioning

confidence: 99%

A Sino-Germanλ6 cm polarization survey of the Galactic plane

Gao

Reich²,

Han

et al. 2010

A&A

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Context. Linearly polarized Galactic synchrotron emission provides valuable information about the properties of the Galactic magnetic field and the interstellar magneto-ionic medium, when Faraday rotation along the line of sight is properly taken into account. Aims. We aim to survey the Galactic plane at λ6 cm including linear polarization. At such a short wavelength Faraday rotation effects are in general small and the Galactic magnetic field properties can be probed to larger distances than at long wavelengths. Methods. The Urumqi 25-m telescope is used for a sensitive λ6 cm survey in total and polarized intensities. WMAP K-band (22.8 GHz) polarization data are used to restore the absolute zero-level of the Urumqi U and Q maps by extrapolation. Results. Total intensity and polarization maps are presented for a Galactic plane region of 129 • ≤ ≤ 230 • and |b| ≤ 5 • in the anti-centre with an angular resolution of 9. 5 and an average sensitivity of 0.6 mK and 0.4 mK T B in total and polarized intensity, respectively. We briefly discuss the properties of some extended Faraday Screens detected in the λ6 cm polarization maps. Conclusions. The Sino-German λ6 cm polarization survey provides new information about the properties of the magnetic ISM. The survey also adds valuable information for discrete Galactic objects and is in particular suited to detect extended Faraday Screens with large rotation measures hosting strong regular magnetic fields.

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On Large-Scale Magnetic Field Reversals in the Outer Galaxy

Cited by 50 publications

References 22 publications

The large-scale magnetic field in the fourth Galactic quadrant

The large-scale magnetic field in the fourth Galactic quadrant

Rotation Measures of Extragalactic Sources behind the Southern Galactic Plane: New Insights into the Large‐Scale Magnetic Field of the Inner Milky Way

A Sino-Germanλ6 cm polarization survey of the Galactic plane

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