Diffusion of cosmic-ray electrons in M 51 observed with LOFAR at 54 MHz

Abstract

Context. The details of cosmic-ray transport have a strong impact on galaxy evolution. The peak of the cosmic-ray energy distribution is observable in the radio continuum using the electrons as proxy. Aims. We measure the length that the cosmic-ray electrons (CRE) are transported during their lifetime in the nearby galaxy M 51 across one order of magnitude in cosmic-ray energy (approximately 1-10 GeV). To this end we use new ultra-low frequency observations from the LOw Frequency ARay (LOFAR) at 54 MHz and ancillary data between 144 and 8350 MHz. Methods. As the the CRE originate from supernova remnants, the radio maps are smoothed in comparison to the distribution of the star formation. By convolving the map of the star-formation rate (SFR) surface density with a Gaussian kernel, we can linearise the radio-SFR relation. The best-fitting convolution kernel is then our estimate of the CRE transport length. Results. We find that the CRE transport length increases at low frequencies, as expected since the CRE have longer lifetimes. The CRE transport length is $l_{\mathrm{CRE}}=\sqrt{4D{t}_{\mathrm{syn}}}$, where $D$ is the isotropic diffusion coefficient and $t_{\mathrm{syn}}$ is the CRE lifetime as given by synchrotron and inverse Compton losses. We find that the data can be well fitted by diffusion, where $D=(2.14\pm 0.13)\times 10^{28}\mathrm{c}{\mathrm{m}}^2{\mathrm{s}}^{-1}$. With $D\propto E^{0.001\pm 0.185}$, the diffusion coefficient is independent of the CRE energy $E$ in the range considered. Conclusions. Our results suggest that the transport of GeV-cosmic ray electrons in the star-forming discs of galaxies is governed by energy-independent diffusion.

Accepted to Astronomy and Astrophysics. 11 pages, 5 figures, 2 tables

References in corpus (37)

• The Circumgalactic Medium
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The LOFAR Two-metre Sky Survey -- V. Second data release
• Cool Outflows in Galaxies and their Implications
• Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field
• The Radio Spectral Energy Distribution and Star Formation Rate Calibration in Galaxies
• AMS-02 beryllium data and its implication for cosmic ray transport
• Connecting Far-Infrared and Radio Morphologies of Disk Galaxies: Cosmic-Ray Electron Diffusion After Star Formation Episodes
• High-resolution radio continuum survey of M33 II. Thermal and nonthermal emission
• The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR
• The LOFAR LBA Sky Survey I. survey description and preliminary data release
• The LOFAR Two-metre Sky Survey Deep fields: The star formation rate - radio luminosity relation at low frequencies
• The Radio Continuum-Star Formation Rate Relation in WSRT SINGS Galaxies
• The dependence of cosmic ray driven galactic winds on halo mass
• Cosmic ray transport in starburst galaxies
• The Westerbork SINGS Survey: I. Overview and Image Atlas
• Radio haloes in nearby galaxies modelled with 1D cosmic-ray transport using SPINNAKER
• Charged particle diffusion in isotropic random magnetic fields
• Synchrotron spectral index and interstellar medium densities of star-forming galaxies
• Reconciling cosmic-ray transport theory with phenomenological models motivated by Milky-Way data
• Regimes of cosmic-ray diffusion in Galactic turbulence
• Nearby galaxies in LoTSS-DR2: insights into the non-linearity of the radio-SFR relation
• CHANG-ES XIII: Transport processes and the magnetic fields of NGC 4666 - indication of a reversing disk magnetic field
• Relative distribution of cosmic rays and magnetic fields
• Cosmic rays and non-thermal emission in simulated galaxies. I. Electron and proton spectra compared to Voyager-1 data
• CHANG-ES XXIII: Influence of a galactic wind in NGC 5775
• Cosmic rays across the star-forming galaxy sequence. I: Cosmic ray pressures and calorimetry
• The radio continuum perspective on cosmic-ray transport in external galaxies
• Turbulent diffusion of streaming cosmic rays in compressible, partially ionised plasma
• A hydrodynamical study of outflows in starburst galaxies with different driving mechanisms
• Deciphering the radio-star formation correlation on kpc-scales I. Adaptive kernel smoothing experiments
• The magnetized disk-halo transition region of M51
• Nearby galaxies in the LOFAR Two-metre Sky Survey II. The magnetic field-gas relation
• Metal-THINGS: On the metallicity and ionization of ULX sources in NGC 925
• Studying the local magnetic field and anisotropy of magnetic turbulence by synchrotron polarization derivative
• Cosmic-ray electron transport in the galaxy M 51
• Diffusion coefficient with displacement variance of energetic particles with adiabatic focusing

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