S-PASS/ATCA: a window on the magnetic universe in the Southern hemisphere

Schnitzeler, Dominic; Carretti, E.; Wieringa, M.; Gaensler, B. M.; Haverkorn, M.; Poppi, S.

doi:10.1093/mnras/stz092

Cited by 29 publications

(38 citation statements)

References 61 publications

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“…The solar field also oscillates with a ∼ 22 yr period. Exponential growth rates of the various eigenmodes in 1-D dynamo solutions for a thin [84,85] slab and a spherical shell were presented in Sec. 6 of Brandenburg and Subramanian [17].…”

Section: Parity Of the Fieldmentioning

confidence: 99%

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

et al. 2019

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Constraining dynamo theories of magnetic field origin by observation is indispensable but challenging, in part because the basic quantities measured by observers and predicted by modelers are different. We clarify these differences and sketch out ways to bridge the divide. Based on archival and previously unpublished data, we then compile various important properties of galactic magnetic fields for nearby spiral galaxies. We consistently compute strengths of total, ordered, and regular fields, pitch angles of ordered and regular fields, and we summarize the present knowledge on azimuthal modes, field parities, and the properties of non-axisymmetric spiral features called magnetic arms. We review related aspects of dynamo theory, with a focus on mean-field models and their predictions for large-scale magnetic fields in galactic discs and halos. Further, we measure the velocity dispersion of H I gas in arm and inter-arm regions in three galaxies, M 51, M 74, and NGC 6946, since spiral modulation of the root-mean-square turbulent speed has been proposed as a driver of non-axisymmetry in large-scale dynamos. We find no evidence for such a modulation and place upper limits on its strength, helping to narrow down the list of mechanisms to explain magnetic arms. Successes and remaining challenges of dynamo models with respect to explaining observations are briefly summarized, and possible strategies are suggested. With new instruments like the Square Kilometre Array (SKA), large data sets of magnetic and non-magnetic properties from thousands of galaxies will become available, to be compared with theory.

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Section: Parity Of the Fieldmentioning

confidence: 99%

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

et al. 2019

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“…For the first condition, large-scale Galactic magnetic field measurements exist (e.g. Han et al 2006;Brown et al 2007;Mao et al 2010;Nota & Katgert 2010;Van Eck et al 2011;Schnitzeler et al 2019), and suggest that a large-scale coherent field does exist within the Milky Way disk. Exploring the second and third conditions are part of the motivation of the MAGMO project.…”

Section: Field Direction Comparison With Large-scale Fields Determinementioning

confidence: 99%

MAGMO: polarimetry of 1720-MHz OH masers towards southern star-forming regions

Ogbodo

Green

Dawson

et al. 2020

Monthly Notices of the Royal Astronomical Society

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From targeted observations of ground-state OH masers towards 702 Multibeam (MMB) survey 6.7-GHz methanol masers, between Galactic longitudes 186 • through the Galactic centre to 20 • , made as part of the 'MAGMO' project, we present the physical and polarisation properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star formation regions. In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from −11.4 to +13.2 mG, and a median magnetic field strength of |B LOS | ∼ 6 mG. With limited statistics, we present the in-situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers and water masers, and compare maser positions with mid-infrared images of the parent star forming regions. Of the 33 1720-MHz star formation masers, ten are offset from their central exciting sources, and appear to be associated with outflow activity.

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“…Since increasing the number of models improves the quality of the fit by increasing the number of free parameters [principle of parsimony; 36], statistical measures, such as, the Bayesian inference criterion and/or Akaike information criterion are used to limit the number of models or to choose between degenerate fits [6,37]. However, Stokes Q, U fitting has the advantage of also fitting for the spectral index of the polarized flux density [see 37], which is not possible in RM synthesis and is one of the origins of complexity in the Faraday depth spectrum [e.g., 21,37].…”

Section: Common Spectro-polarimetric Data Analysis Techniquesmentioning

confidence: 99%

An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

et al. 2019

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In this paper we present a detailed analysis of the Faraday depth (FD) spectrum and its clean components obtained through the application of the commonly used technique of Faraday rotation measure synthesis to analyze spectro-polarimetric data. In order to directly compare the Faraday depth spectrum with physical properties of a magneto-ionic medium, we generated synthetic broad-bandwidth spectro-polarimetric observations from magnetohydrodynamic (MHD) simulations of a transonic, isothermal, compressible turbulent medium. We find that correlated magnetic field structures give rise to a combination of spiky, localized peaks at certain FD values, and broad structures in the FD spectrum. Although the majority of these spiky FD structures appear narrow, giving an impression of a Faraday thin medium, we show that they arise from strong synchrotron emissivity at that FD. Strong emissivity at a FD can arise because of both strong spatially-local polarized synchrotron emissivity at a FD or accumulation of weaker emissions along the distance through a medium that have Faraday depths within half the width of the rotation measure spread function. Such a complex Faraday depth spectrum is a natural consequence of MHD turbulence when the lines of sight pass through a few turbulent cells. This therefore complicates the convention of attributing narrow FD peaks to presence of a Faraday rotating medium along the line of sight. Our work shows that it is difficult to extract the FD along a line of sight from the Faraday depth spectrum using standard methods for a turbulent medium in which synchrotron emission and Faraday rotation occur simultaneously. of 30medium for a large number of sources in a much reduced amount of observing time. Broad-band spectro-polarimetry has played a crucial role in unveiling the properties of magnetic fields in nearby galaxies [1][2][3], in high redshift galaxies [4,5], in active galactic nuclei [AGN; 6-8] and the intergalactic medium [9]. In order to physically interpret such data, the technique of Faraday rotation measure (RM) synthesis [10,11] and direct fitting of the Stokes Q and U spectra of a polarized source with models of the magneto-ionic media, known as Stokes Q, U fitting [6,12,13] have been developed. It is often not straightforward to interpret the results from these techniques and connect them to the physical properties of the magnetized plasmas being investigated [14].Currently, several large-scale spectro-polarimetric campaigns are underway, mostly in the 1 to 5 GHz frequency range. On one hand, dedicated surveys with interferometers are being conducted to study the broad-band polarization properties of millions of extragalactic sources. For example, the Karl G. Jansky Very Large Array Sky Survey [VLASS; 15,16], the Polarization Sky Survey of the Universe's Magnetism [POSSUM; 17], the QU Observations at Cm wavelength with Km baselines using ATCA 1 (QUOCKA), the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey [18], and the recent LOFAR Two-meter Sky Survey [L...

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S-PASS/ATCA: a window on the magnetic universe in the Southern hemisphere

Cited by 29 publications

References 61 publications

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

MAGMO: polarimetry of 1720-MHz OH masers towards southern star-forming regions

An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

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