Magnetic fields and spiral arms in the galaxy M51

Fletcher, Andrew; Beck, Rainer; Shukurov, Anvar; Berkhuijsen, E. M.; Horellou, C.

doi:10.1111/j.1365-2966.2010.18065.x

Cited by 269 publications

(464 citation statements)

References 48 publications

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“…These include VLA observations covered in Fletcher et al (2011) at 1.4 GHz and 4.8 GHz, and LO-FAR High Band Antenna (HBA) observations (151 MHz) from Mulcahy et al (2014). Details of these observations and their data reduction are described in the respective papers.…”

Section: Observational Datamentioning

confidence: 99%

“…Data at 151 MHz (Mulcahy et al 2014), 333 MHz (this work), 1.4 GHz, and 4.8 GHz (Fletcher et al 2011) were used. Background point sources were removed by fitting Gaussians to them before measuring the radial profile.…”

Section: Radio Continuum Scale Lengthsmentioning

confidence: 99%

“…In Sect. 3 we present the observational data used in this work, the Very Large Array (VLA) maps at 1.4 GHz and 4.8 GHz Fletcher et al (2011), LOw Frequency ARray (LOFAR) map at 151 MHz (Mulcahy et al 2014), and our new GMRT map at Tully (1974); (b) Ciardullo et al (2002); (c) Bigiel et al (2010).…”

Section: Introductionmentioning

confidence: 99%

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Modelling the cosmic ray electron propagation in M 51

Mulcahy

Fletcher

Beck

et al. 2016

A&A

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Context. Cosmic ray electrons (CREs) are a crucial part of the interstellar medium and are observed via synchrotron emission. While much modelling has been carried out on the CRE distribution and propagation of the Milky Way, little has been done on normal external star-forming galaxies. Recent spectral data from a new generation of radio telescopes enable us to find more robust estimations of the CRE propagation. Aims. To model the synchrotron spectral index of M 51 using the diffusion energy-loss equation and to compare the model results with the observed spectral index determined from recent low-frequency observations with LOFAR. Methods. We solve the time-dependent diffusion energy-loss equation for CREs in M 51. This is the first time that this model for CRE propagation has been solved for a realistic distribution of CRE sources, which we derive from the observed star formation rate, in an external galaxy. The radial variation of the synchrotron spectral index and scale-length produced by the model are compared to recent LOFAR and older VLA observational data and also to new observations of M 51 at 325 MHz obtained with the GMRT. Results. We find that propagation of CREs by diffusion alone is sufficient to reproduce the observed spectral index distribution in M 51. An isotropic diffusion coefficient with a value of 6.6 ± 0.2 × 10 28 cm 2 s −1 is found to fit best and is similar to what is seen in the Milky Way. We estimate an escape time of 11 Myr from the central galaxy to 88 Myr in the extended disk. It is found that an energy dependence of the diffusion coefficient is not important for CRE energies in the range 0.01 GeV-3 GeV. We are able to reproduce the dependence of the observed synchrotron scale-lengths on frequency, with l ∝ ν −1/4 in the outer disk and l ∝ ν −1/8 in the inner disk.

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Section: Observational Datamentioning

confidence: 99%

Section: Radio Continuum Scale Lengthsmentioning

confidence: 99%

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Modelling the cosmic ray electron propagation in M 51

Mulcahy

Fletcher

Beck

et al. 2016

A&A

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“…12d). Moreover, B ord is not related to the SFR (Frick et al 2001;Chyży 2008;Krause 2009;Tabatabaei et al 2013), but is controlled by various dynamical and environmental effects (Fletcher et al 2011). Thus it is expected that l dif does not directly scale with Σ SFR .…”

Section: Comparison With Other Galaxiesmentioning

confidence: 99%

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

Tabatabaei

Berkhuijsen

Frick

et al. 2013

A&A

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Interstellar magnetic fields and the propagation of cosmic ray electrons have an important impact on the radio-infrared (IR) correlation in galaxies. This becomes evident when studying different spatial scales within galaxies. We investigate the correlation between the IR and free-free/synchrotron radio continuum emission at 20 cm from the two local group galaxies M 31 and M 33 on spatial scales between 0.4 and 10 kpc. The multi-scale radio-IR correlations have been carried out using a wavelet analysis. The free-free and IR emission are correlated on all scales, but on some scales the synchrotron emission is only marginally correlated with the IR emission. The synchrotron-IR correlation is stronger in M 33 than in M 31 on small scales (<1 kpc), but it is weaker than in M 31 on larger scales. Taking the smallest scale on which the synchrotron-IR correlation exists as the propagation length of cosmic ray electrons, we show that the difference on small scales can be explained by the smaller propagation length in M 33 than in M 31. On large scales, the difference is due to the thick disk/halo in M 33, which is absent in M 31. A comparison of our data with data on NGC 6946, the LMC and M 51 suggests that the propagation length is determined by the ratio of ordered-to-turbulent magnetic field strength, which is consistent with diffusion of CR electrons in the ISM. As the diffusion length of CR electrons influences the radio-IR correlation, this dependence is a direct observational evidence of the importance of magnetic fields for the radio-IR correlation within galaxies. The star-formation rate per surface area only indirectly influences the diffusion length as it increases the strength of the turbulent magnetic field.

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“…The images of polarization angles in two or more wavelengths have often been used to derive rotation measure maps and study the magnetic field structure (e.g. Berkhuijsen et al 2003, Fletcher et al 2011. Polarization maps with marginal significance (3-5σ) in most areas can produce an RM map but only significant in some area, not everywhere (e.g.…”

Section: Diffuse Radio Polarized Emissionmentioning

confidence: 99%

Magnetic fields in our Milky Way Galaxy and nearby galaxies

Han

2012

Proc. IAU

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Abstract. Magnetic fields in our Galaxy and nearby galaxies have been revealed by starlight polarization, polarized emission from dust grains and clouds at millimeter and submillimeter wavelength, the Zeeman effect of spectral lines or maser lines from clouds or clumps, diffuse radio synchrotron emission from relativistic electrons in interstellar magnetic fields, and the Faraday rotation of background radio sources as well as pulsars for our Milky Way. It is easy to get a global structure for magnetic fields in nearby galaxies, while we have observed many details of magnetic fields in our Milky Way, especially by using pulsar rotation measure data. In general, magnetic fields in spiral galaxies probably have a large-scale structure. The fields follow the spiral arms with or without the field direction reversals. In the halo of spiral galaxies magnetic fields exist and probably also have a large-scale structure as toroidal and poloidal fields, but seem to be slightly weaker than those in the disk. In the central region of some galaxies, poloidal fields have been detected as vertical components. Magnetic field directions in galaxies seem to have been preserved during cloud formation and star formation, from large-scale diffuse interstellar medium to molecular clouds and then to the cloud cores in star formation regions or clumps for the maser spots. Magnetic fields in galaxies are passive to dynamics.

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Magnetic fields and spiral arms in the galaxy M51

Cited by 269 publications

References 48 publications

Modelling the cosmic ray electron propagation in M 51

Modelling the cosmic ray electron propagation in M 51

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

Magnetic fields in our Milky Way Galaxy and nearby galaxies

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