How cosmic ray electron propagation affects radio–far-infrared correlations in M 31 and M 33

Berkhuijsen, E. M.; Beck, Rainer; Tabatabaei, F. S.

doi:10.1093/mnras/stt1400

Cited by 68 publications

(77 citation statements)

References 67 publications

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“…The wavelength-dependent distributions (Fig. 12 left) can also be understood as the result of CRE diffusion, as suggested previously by Basu & Roy (2013), Tabatabaei et al (2013a), and Berkhuijsen et al (2013).…”

Section: Propagation Of Cosmic-ray Electronssupporting

confidence: 73%

Magnetic fields in the nearby spiral galaxy IC 342: A multi-frequency radio polarization study

Beck

2015

A&A

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Context. Magnetic fields play an important role in the formation and stabilization of spiral structures in galaxies, but the interaction between interstellar gas and magnetic fields has not yet been understood. In particular, the phenomenon of "magnetic arms" located between material arms is a mystery. Aims. The strength and structure of interstellar magnetic fields and their relation to spiral arms in gas and dust are investigated in the nearby and almost face-on spiral galaxy IC 342. Methods. The total and polarized radio continuum emission of IC 342 was observed with high spatial resolution in four wavelength bands with the Effelsberg and VLA telescopes. At λ6.2 cm the data from both telescopes were combined. I separated thermal and nonthermal (synchrotron) emission components with the help of the spectral index distribution and derived maps of the magnetic field strength, degree of magnetic field order, magnetic pitch angle, Faraday rotation measure, and Faraday depolarization. Results. IC 342 hosts a diffuse radio disk with an intensity that decreases exponentially with increasing radius. The frequency dependence of the scalelength of synchrotron emission indicates energy-dependent propagation of the cosmic-ray electrons, probably via the streaming instability. The equipartition strength of the total field in the main spiral arms is typically 15 μG, that of the ordered field about 5 μG. The total radio emission, observed with the VLA's high resolution, closely follows the dust emission in the infrared at 8 μm (Spitzer telescope) and 22 μm (WISE telescope). The polarized emission is not diffuse, but concentrated in spiral arms of various types: (1) a narrow arm of about 300 pc width, displaced inwards with respect to the eastern arm by about 200 pc, indicating magnetic fields compressed by a density wave; (2) a broad arm of 300-500 pc width around the northern arm with systematic variations in polarized emission, polarization angles, and Faraday rotation measures on a scale of about 2 kpc, indicative of a helically twisted flux tube generated by the Parker instability; (3) a rudimentary magnetic arm in an interarm region in the north-west; (4) several broad spiral arms in the outer galaxy, related to spiral arms in the total neutral gas; (5) short features in the outer south-western galaxy, probably distorted by tidal interaction. Faraday rotation of the polarization angles reveals an underlying regular field of only 0.5 μG strength with a large-scale axisymmetric spiral pattern, probably a signature of a mean-field α − Ω dynamo, and an about 10× stronger field that fluctuates on scales of a few 100 pc. The magnetic field around the bar in the central region of IC 342 resembles that of large barred galaxies; it has a regular spiral pattern with a large pitch angle, is directed outwards, and is opposite to the large-scale regular field in the disk. Polarized emission at λ20.1 cm is strongly affected by Faraday depolarization in the western and northern parts of the galaxy. Helical fields extending fro...

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Section: Propagation Of Cosmic-ray Electronssupporting

confidence: 73%

Magnetic fields in the nearby spiral galaxy IC 342: A multi-frequency radio polarization study

Beck

2015

A&A

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“…There is evidence that the assumption does not hold on sub-kpc scales in the Milky Way (Stepanov et al 2014). That equipartition does not hold on small scales is the direct effect of CR diffusion, as was shown for M31 by Berkhuijsen et al (2013). On the other hand, we have just seen that moving from a model with B = 10 µG at all radii to a model with a strong dependence of B on radius had little effect on the spectral index profile.…”

Section: Model With Energy Losses and Varying Magnetic Field Strengthsupporting

confidence: 57%

“…The difference in spectral index is not constant; it varies from 0.08 in the central region of M 51 to 0.16 at around 11 kpc. Berkhuijsen et al (2013) showed that in M 31, unlike other galaxies, most of the CREs are confined to a thin non-thermal disk with an exponential scale height of 0.3 ∼ 0.4 kpc at 1.4 GHz, whereas in M 33 many CREs move out of the thin disk into a thick disk / halo with scale height of ∼2 kpc at 1.4 GHz. It was also found that the diffusion coefficient was ten times greater in M 33 than M 31.…”

Section: Vertical Escape Of Cres By Diffusionmentioning

confidence: 97%

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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“…The upper bounds of the total energy flux are S ≤ 4.2 × 10 −14 erg cm −2 s −1 (for 3.6 cm) and S ≤ 3.6 × 10 −14 erg cm −2 s −1 (for 20 cm). The magnetic field strength of M33 is B = 8.1 ± 0.5 µG [19]. This large magnetic field strength ensures that the synchrotron radiation dominates the cooling rate of the electron and positron pairs.…”

Section: Radio Observations Of M33mentioning

confidence: 99%

Constraining annihilating dark matter by radio data of M33

Chan

2017

Phys. Rev. D

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Recent studies of radio data put strong constraints on annihilation cross section for dark matter. In this article, we provide the first analysis of using M33 radio data in constraining annihilating dark matter. The resulting constraints of annihilation cross sections for some channels are more stringent than that obtained from 6 years of Fermi Large Area Telescope (Fermi-LAT) gamma-ray observations of the Milky Way dwarf spheroidal satellite galaxies. In particular, the conservative lower limits of dark matter mass annihilating via $e^+e^-$, $\mu^+\mu^-$and $\tau^+\tau^-$ channels are 190 GeV, 120 GeV and 70 GeV respectively with the thermal relic annihilation cross section. These results are in large tensions with some of the recent quantitative analyses of the AMS-02 and Fermi-LAT data of the Milky Way center.Comment: Accepted for publication in Phy. Rev.

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How cosmic ray electron propagation affects radio–far-infrared correlations in M 31 and M 33

Cited by 68 publications

References 67 publications

Magnetic fields in the nearby spiral galaxy IC 342: A multi-frequency radio polarization study

Magnetic fields in the nearby spiral galaxy IC 342: A multi-frequency radio polarization study

Modelling the cosmic ray electron propagation in M 51

Constraining annihilating dark matter by radio data of M33

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