| 1. |
- André, Ph., et al.
(author)
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Probing the cold magnetised Universe with SPICA-POL (B-BOP)
- 2019
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In: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 36
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Research review (peer-reviewed)abstract
- Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the cryogenic infrared space telescope recently pre-selected for a 'Phase A' concept study as one of the three remaining candidates for European Space Agency (ESA's) fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager [SPICA-POL, now called B-fields with BOlometers and Polarizers (B-BOP)], which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetised Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100-350 mu m images of linearly polarised dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 mu m images will also have a factor similar to 30 higher resolution than Planck polarisation data. This will make B-BOP a unique tool for characterising the statistical properties of the magnetised ISM and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing Galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.
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| 2. |
- Fougeres, Chloe, et al.
(author)
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Search for Na-22 in novae supported by a novel method for measuring femtosecond nuclear lifetimes
- 2023
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- Classical novae are thermonuclear explosions in stellar binary systems, and important sources of Al-26 and Na-22. While ? rays from the decay of the former radioisotope have been observed throughout the Galaxy, Na-22 remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV ?-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The Na-22(p, ?)Mg-23 reaction remains the only source of large uncertainty about the amount of Na-22 ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in Mg-23. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the Mg-23 states, places strong limits on the amount of Na-22 produced in novae and constrains its detectability with future space-borne observatories. The authors report a particle-particle correlation and velocity-difference profile method to measure nuclear lifetime. The results obtained for excited states of 23Mg are used to constrain the production of 22Na in the astrophysical novae explosions.
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| 3. |
- Aghanim, N., et al.
(author)
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Planck 2018 results XII. Galactic astrophysics using polarized dust emission
- 2020
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 641
-
Journal article (peer-reviewed)abstract
- Observations of the submillimetre emission from Galactic dust, in both total intensity I and polarization, have received tremendous interest thanks to the Planck full-sky maps. In this paper we make use of such full-sky maps of dust polarized emission produced from the third public release of Planck data. As the basis for expanding on astrophysical studies of the polarized thermal emission from Galactic dust, we present full-sky maps of the dust polarization fraction p, polarization angle psi, and dispersion function of polarization angles ?. The joint distribution (one-point statistics) of p and N-H confirms that the mean and maximum polarization fractions decrease with increasing N-H. The uncertainty on the maximum observed polarization fraction, (max) = 22.0(-1.4)(+3.5) p max = 22 . 0 - 1.4 + 3.5 % at 353 GHz and 80 ' resolution, is dominated by the uncertainty on the Galactic emission zero level in total intensity, in particular towards diffuse lines of sight at high Galactic latitudes. Furthermore, the inverse behaviour between p and ? found earlier is seen to be present at high latitudes. This follows the ?proportional to p(-1) relationship expected from models of the polarized sky (including numerical simulations of magnetohydrodynamical turbulence) that include effects from only the topology of the turbulent magnetic field, but otherwise have uniform alignment and dust properties. Thus, the statistical properties of p, psi, and ? for the most part reflect the structure of the Galactic magnetic field. Nevertheless, we search for potential signatures of varying grain alignment and dust properties. First, we analyse the product map ?xp, looking for residual trends. While the polarization fraction p decreases by a factor of 3-4 between N-H=10(20) cm(-2) and N-H=2x10(22) cm(-2), out of the Galactic plane, this product ?xp only decreases by about 25%. Because ? is independent of the grain alignment efficiency, this demonstrates that the systematic decrease in p with N-H is determined mostly by the magnetic-field structure and not by a drop in grain alignment. This systematic trend is observed both in the diffuse interstellar medium (ISM) and in molecular clouds of the Gould Belt. Second, we look for a dependence of polarization properties on the dust temperature, as we would expect from the radiative alignment torque (RAT) theory. We find no systematic trend of ?xp with the dust temperature T-d, whether in the diffuse ISM or in the molecular clouds of the Gould Belt. In the diffuse ISM, lines of sight with high polarization fraction p and low polarization angle dispersion ? tend, on the contrary, to have colder dust than lines of sight with low p and high ?. We also compare the Planck thermal dust polarization with starlight polarization data in the visible at high Galactic latitudes. The agreement in polarization angles is remarkable, and is consistent with what we expect from the noise and the observed dispersion of polarization angles in the visible on the scale of the Planck beam. The two polarization emission-to-extinction ratios, R-P/p and R-S/V, which primarily characterize dust optical properties, have only a weak dependence on the column density, and converge towards the values previously determined for translucent lines of sight. We also determine an upper limit for the polarization fraction in extinction, p(V)/E(B-V), of 13% at high Galactic latitude, compatible with the polarization fraction p approximate to 20% observed at 353 GHz. Taken together, these results provide strong constraints for models of Galactic dust in diffuse gas.
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| 4. |
- Akrami, Y., et al.
(author)
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Planck 2018 results : XI. Polarized dust foregrounds
- 2020
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In: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 641
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Journal article (peer-reviewed)abstract
- The study of polarized dust emission has become entwined with the analysis of the cosmic microwave background (CMB) polarization in the quest for the curl-like B-mode polarization from primordial gravitational waves and the low-multipole E-mode polarization associated with the reionization of the Universe. We used the new Planck PR3 maps to characterize Galactic dust emission at high latitudes as a foreground to the CMB polarization and use end-to-end simulations to compute uncertainties and assess the statistical significance of our measurements. We present PlanckEE, BB, and TE power spectra of dust polarization at 353 GHz for a set of six nested high-Galactic-latitude sky regions covering from 24 to 71% of the sky. We present power-law fits to the angular power spectra, yielding evidence for statistically significant variations of the exponents over sky regions and a difference between the values for the EE and BB spectra, which for the largest sky region are alpha (EE)=-2.42 +/- 0.02 and alpha (BB)=-2.54 +/- 0.02, respectively. The spectra show that the TE correlation and E/B power asymmetry discovered by Planck extend to low multipoles that were not included in earlier Planck polarization papers due to residual data systematics. We also report evidence for a positive TB dust signal. Combining data from Planck and WMAP, we have determined the amplitudes and spectral energy distributions (SEDs) of polarized foregrounds, including the correlation between dust and synchrotron polarized emission, for the six sky regions as a function of multipole. This quantifies the challenge of the component-separation procedure that is required for measuring the low-l reionization CMB E-mode signal and detecting the reionization and recombination peaks of primordial CMB B modes. The SED of polarized dust emission is fit well by a single-temperature modified black-body emission law from 353 GHz to below 70 GHz. For a dust temperature of 19.6 K, the mean dust spectral index for dust polarization is beta (P)(d) = 1.53 +/- 0.02 beta d P = 1.53 +/- 0.02 . The difference between indices for polarization and total intensity is beta (P)(d)-beta (I)(d) = 0.05 +/- 0.03 beta d P - beta d I =0.05 +/- 0.03 . By fitting multi-frequency cross-spectra between Planck data at 100, 143, 217, and 353 GHz, we examine the correlation of the dust polarization maps across frequency. We find no evidence for a loss of correlation and provide lower limits to the correlation ratio that are tighter than values we derive from the correlation of the 217- and 353 GHz maps alone. If the Planck limit on decorrelation for the largest sky region applies to the smaller sky regions observed by sub-orbital experiments, then frequency decorrelation of dust polarization might not be a problem for CMB experiments aiming at a primordial B-mode detection limit on the tensor-to-scalar ratio r similar or equal to 0.01 at the recombination peak. However, the Planck sensitivity precludes identifying how difficult the component-separation problem will be for more ambitious experiments targeting lower limits on r.
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| 5. |
- Bracco, Andrea, et al.
(author)
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Is there a left-handed magnetic field in the solar neighborhood? : Exploring helical magnetic fields in the interstellar medium through dust polarization power spectra
- 2019
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 621
-
Journal article (peer-reviewed)abstract
- Context. The analysis of the full-sky Planck polarization data at 850 mu m revealed unexpected properties of the E- and B-mode power spectra of dust emission in the interstellar medium (ISM). The positive cross-correlations over a wide range of angular scales between the total dust intensity, T, and both E and (most of all) B modes has raised new questions about the physical mechanisms that affect dust polarization, such as the Galactic magnetic field structure. This is key both to better understanding ISM dynamics and to accurately describing Galactic foregrounds to the polarization of the cosmic microwave background (CMB). In particular, in the quest to find primordial B modes of the CMB, the observed positive cross-correlation between T and B for interstellar dust requires further investigation towards parity-violating processes in the ISM. Aims. In this theoretical paper we investigate the possibility that the observed cross-correlations in the dust polarization power spectra, and specifically the one between T and B, can be related to a parity-odd quantity in the ISM such as the magnetic helicity. Methods. We produce synthetic dust polarization data, derived from 3D analytical toy models of density structures and helical magnetic fields, to compare with the E and B modes of observations. We present several models. The first is an ideal fully helical isotropic case, such as the Arnold-Beltrami-Childress field. Second, following the nowadays favored interpretation of the T-E signal in terms of the observed alignment between the magnetic field morphology and the filamentary density structure of the diffuse ISM, we design models for helical magnetic fields wrapped around cylindrical interstellar filaments. Lastly, focusing on the observed T-B correlation, we propose a new line of interpretation of the Planck observations advocating the presence of a large-scale helical component of the Galactic magnetic field in the solar neighborhood. Results. Our analysis shows that: I) the sign of magnetic helicity does not affect E and B modes for isotropic magnetic-field configurations; II) helical magnetic fields threading interstellar filaments cannot reproduce the Planck results; and III) a weak helical left-handed magnetic field structure in the solar neighborhood may explain the T-B correlation seen in the Planck data. Such a magnetic-field configuration would also account for the observed large-scale T-E correlation. Conclusions. This work suggests a new perspective for the interpretation of the dust polarization power spectra that supports the imprint of a large-scale structure of the Galactic magnetic field in the solar neighborhood.
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| 6. |
- Brandenburg, Axel, et al.
(author)
-
E and B Polarizations from Inhomogeneous and Solar Surface Turbulence
- 2019
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In: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 870:2
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Journal article (peer-reviewed)abstract
- Gradient- and curl-type or E- and B-type polarizations have been routinely analyzed to study the physics contributing to the cosmic microwave background polarization and galactic foregrounds. They characterize the parity-even and parity-odd properties of the underlying physical mechanisms, such as, for example, hydromagnetic turbulence in the case of dust polarization. Here, we study spectral correlation functions characterizing the parity-even and parity-odd parts of linear polarization for homogeneous and inhomogeneous turbulence to show that only the inhomogeneous helical case can give rise to a parity-odd polarization signal. We also study nonhelical turbulence and suggest that a strong non-vanishing (here negative) skewness of the E polarization is responsible for an enhanced ratio of the EE to the BB (quadratic) correlation in both the helical and nonhelical cases. This could explain the enhanced EE/BB ratio observed recently for dust polarization. We close with a preliminary assessment of using the linear polarization of the Sun to characterize its helical turbulence without being subjected to the pi ambiguity that magnetic inversion techniques have to address.
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| 7. |
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| 8. |
- Heald, G., et al.
(author)
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Magnetism science with the square kilometre array
- 2020
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In: Galaxies. - : MDPI AG. - 2075-4434. ; 8:8
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Journal article (peer-reviewed)abstract
- The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
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| 9. |
- Heesen, V., et al.
(author)
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Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation
- 2023
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 670
-
Journal article (peer-reviewed)abstract
- Context. The existence of magnetic fields in the circumgalactic medium (CGM) is largely unconstrained. Their detection is important as magnetic fields can have a significant impact on the evolution of the CGM, and, in turn, the fields can serve as tracers for dynamical processes in the CGM. Aims. Using the Faraday rotation of polarised background sources, we aim to detect a possible excess of the rotation measure in the surrounding area of nearby galaxies. Methods. We used 2461 residual rotation measures (RRMs) observed with the LOw Frequency ARray (LOFAR), where the foreground contribution from the Milky Way is subtracted. The RRMs were then studied around a subset of 183 nearby galaxies that was selected by apparent B-band magnitude. Results. We find that, in general, the RRMs show no significant excess for small impact parameters (i.e., the perpendicular distance to the line of sight). However, if we only consider galaxies at higher inclination angles and sightlines that pass close to the minor axis of the galaxies, we find significant excess at impact parameters of less than 100 kpc. The excess in |RRM| is 3.7 rad m-2 with an uncertainty between ±0.9 rad m-2 and ±1.3 rad m-2 depending on the statistical properties of the background (2.8σ - 4.1σ). With electron densities of ∼10-4 cm-3, this suggests magnetic field strengths of a few tenths of a microgauss. Conclusions. Our results suggest a slow decrease in the magnetic field strength with distance from the galactic disc, as expected if the CGM is magnetised by galactic winds and outflows.
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| 10. |
- Levrier, F., et al.
(author)
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Statistics of the polarized submillimetre emission maps from thermal dust in the turbulent, magnetized, diffuse ISM
- 2018
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 614
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Journal article (peer-reviewed)abstract
- Context. The interstellar medium (ISM) is now widely acknowledged to display features ascribable to magnetized turbulence. With the public release of Planck data and the current balloon-borne and ground-based experiments, the growing amount of data tracing the polarized thermal emission from Galactic dust in the submillimetre provides choice diagnostics to constrain the properties of this magnetized turbulence. Aims. We aim to constrain these properties in a statistical way, focussing in particular on the power spectral index βB of the turbulent component of the interstellar magnetic field in a diffuse molecular cloud, the Polaris Flare. Methods. We present an analysis framework based on simulating polarized thermal dust emission maps using model dust density (proportional to gas density nH) and magnetic field cubes, integrated along the line of sight (LOS), and comparing these statistically to actual data. The model fields are derived from fractional Brownian motion (fBm) processes, which allows a precise control of their one-and two-point statistics. The parameters controlling the model are (1)-(2) the spectral indices of the density and magnetic field cubes, (3)-(4) the RMS-to-mean ratios for both fields, (5) the mean gas density, (6) the orientation of the mean magnetic field in the plane of the sky (POS), (7) the dust temperature, (8) the dust polarization fraction, and (9) the depth of the simulated cubes. We explore the nine-dimensional parameter space through a Markov chain Monte Carlo analysis, which yields best-fitting parameters and associated uncertainties. Results. We find that the power spectrum of the turbulent component of the magnetic field in the Polaris Flare molecular cloud scales with wavenumber as k-βB with a spectral index βB = 2.8 ± 0.2. It complements a uniform field whose norm in the POS is approximately twice the norm of the fluctuations of the turbulent component, and whose position angle with respect to the north-south direction is χ0-69°. The density field nH is well represented by a log-normally distributed field with a mean gas density (nH)40 cm-3, a fluctuation ratio σnH/(nH)1.6, and a power spectrum with an index βn=1.7-0.3 +0.4. We also constrain the depth of the cloud to be d 13 pc, and the polarization fraction p0 0.12. The agreement between the Planck data and the simulated maps for these best-fitting parameters is quantified by a χ2 value that is only slightly larger than unity. Conclusions. We conclude that our fBm-based model is a reasonable description of the diffuse, turbulent, magnetized ISM in the Polaris Flare molecular cloud, and that our analysis framework is able to yield quantitative estimates of the statistical properties of the dust density and magnetic field in this cloud.
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| 11. |
- Ritacco, A., et al.
(author)
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NIKA 150 GHz polarization observations of the Crab nebula and its spectral energy distribution
- 2018
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Journal article (peer-reviewed)abstract
- The Crab nebula is a supernova remnant exhibiting a highly polarized synchrotron radiation at radio and millimetre wavelengths. It is the brightest source in the microwave sky with an extension of 7 by 5 arcmin, and is commonly used as a standard candle for any experiment which aims to measure the polarization of the sky. Though its spectral energy distribution has been well characterized in total intensity, polarization data are still lacking at millimetre wavelengths. We report in this paper high resolution observations (18 00 FWHM) of the Crab nebula in total intensity and linear polarization at 150 GHz with the NIKA camera. NIKA, operated at the IRAM 30 m telescope from 2012 to 2015, is a camera made of Lumped Element Kinetic Inductance Detectors (LEKIDs) observing the sky at 150 and 260 GHz. From these observations we are able to reconstruct the spatial distribution of the polarization degree and angle of the Crab nebula, which is found to be compatible with previous observations at lower and higher frequencies. Averaging across the source and using other existing data sets we find that the Crab nebula polarization angle is consistent with being constant over a wide range of frequencies with a value of -87.7 degrees +/- 0.3 in Galactic coordinates. We also present the first estimation of the Crab nebula spectral energy distribution polarized flux in a wide frequency range: 30-353 GHz. Assuming a single power law emission model we find that the polarization spectral index beta(pol) = -0.347 +/- 0.026 is compatible with the intensity spectral index beta = -0.323 +/- 0.001.
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| 12. |
- Shimajiri, Y., et al.
(author)
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Probing accretion of ambient cloud material into the Taurus B211/B213 filament
- 2019
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 623
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Journal article (peer-reviewed)abstract
- Context. Herschel observations have emphasized the role of molecular filaments in star formation. However, the origin and evolution of these filaments are not yet well understood, partly because of the lack of kinematic information. Aims. We confirm from a kinematic viewpoint that the Taurus B211/B213 filament is accreting background cloud material, and we investigate the potential influence of large-scale external effects on the formation of the filament. Methods. To examine whether the B211/B213 filament is accreting background gas because of its gravitational potential, we produced a toy accretion model and compared its predictions to the velocity patterns observed in (CO)-C-12 (1-0) and (CO)-C-13 (1-0). We also examined the spatial distributions of H alpha, Planck 857 GHz dust continuum, and HI emission to search for evidence of large-scale external effects. Results. We estimate that the depth of the Taurus cloud around the B211/B213 filament is similar to 0.3-0.7 pc under the assumption that the density of the gas is the same as the critical density of (CO)-C-13 (1-0). Compared to a linear extent of >10 pc in the plane of the sky, this suggests that the 3D morphology of the cloud surrounding the B211/B213 filament is sheet-like. Position-velocity (PV) diagrams observed in (CO)-C-12 (1-0) and (CO)-C-13 (1-0) perpendicular to the filament axis show that the emission from the gas surrounding B211/B213 is redshifted to the northeast of the filament and blueshifted to the southwest, and that the velocities of both components approach the velocity of the B211/B213 filament as the line of sight approaches the crest of the filament. The PV diagrams predicted by our accretion model are in good agreement with the observed (CO)-C-12 (1-0) and (CO)-C-13 (1-0) PV diagrams, supporting the previously proposed scenario of mass accretion into the filament. Moreover, inspection of the spatial distribution of the H alpha and Planck 857 GHz emission in the Taurus-California-Perseus region on scales up to >200 pc suggests that the B211/B213 filament may have formed as a result of an expanding supershell generated by the Per OB2 association. Conclusions. Based on these results, we propose a scenario in which the B211/B213 filament was initially formed by large-scale compression of HI gas and is now growing in mass by gravitationally accreting molecular gas of the ambient cloud.
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| 13. |
- Šnidariać, Iva, et al.
(author)
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LOFAR Deep Fields: Probing faint Galactic polarised emission in ELAIS-N1
- 2023
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 674
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Journal article (peer-reviewed)abstract
- We present the first deep polarimetric study of Galactic synchrotron emission at low radio frequencies. Our study is based on 21 observations of the European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field using the Low-Frequency Array (LOFAR) at frequencies from 114.9 to 177.4 MHz. These data are a part of the LOFAR Two-metre Sky Survey Deep Fields Data Release 1. We used very low-resolution (4.3') Stokes QU data cubes of this release. We applied rotation measure (RM) synthesis to decompose the distribution of polarised structures in Faraday depth, and cross-correlation RM synthesis to align different observations in Faraday depth. We stacked images of about 150 h of the ELAIS-N1 observations to produce the deepest Faraday cube at low radio frequencies to date, tailored to studies of Galactic synchrotron emission and the intervening magneto-ionic interstellar medium. This Faraday cube covers ∼36 deg2 of the sky and has a noise of 27 μJy PSF-1 RMSF-1 in polarised intensity. This is an improvement in noise by a factor of approximately the square root of the number of stacked data cubes (√20), as expected, compared to the one in a single data cube based on five-to-eight-hour observations. We detect a faint component of diffuse polarised emission in the stacked cube, which was not detected previously. Additionally, we verify the reliability of the ionospheric Faraday rotation corrections estimated from the satellite-based total electron content measurements to be of ∼0.05 Cyrillic small letter GHEad m-2. We also demonstrate that diffuse polarised emission itself can be used to account for the relative ionospheric Faraday rotation corrections with respect to a reference observation.
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| 14. |
- Soler, J. D., et al.
(author)
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The magnetic environment of the Orion-Eridanus superbubble as revealed by Planck
- 2018
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 609
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Journal article (peer-reviewed)abstract
- Using the 353-GHz polarization observations by the Planck satellite we characterize the magnetic field in the Orion-Eridanus super-bubble, a nearby expanding structure that spans more than 1600 square degrees in the sky. We identify a region of both low dispersion of polarization orientations and high polarization fraction associated with the outer wall of the superbubble identified in the most recent models of the large-scale shape of the region. We use the Davis-Chandrasekhar-Fermi method to derive plane-of-the-sky magnetic field strengths of tens of mu G toward the southern edge of the bubble. The comparison of these values with existing Zeeman splitting observations of HI in emission suggests that the large-scale magnetic field in the region was primarily shaped by the expanding superbubble.
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