Loops and spurs: The angular power spectrum of the Galactic synchrotron background

Abstract

We present a new model of the diffuse Galactic synchrotron radiation, concentrating on its angular anisotropies. While previous studies have focussed on either the variation of the emissivity on large (kpc) scales, or on fluctuations due to MHD turbulence in the interstellar medium, we unify these approaches to match the angular power spectrum. We note that the usual turbulence cascade calculation ignores spatial correlations at the injection scale due to compression of the interstellar medium by old supernova remnants -- the 'radio loops', only four of which are visible by eye in radio maps. This new component naturally provides the otherwise missing power on intermediate and small scales in the all-sky map at 408 MHz. Our model can enable more reliable subtraction of the synchrotron foreground for studies of CMB anisotropies (both in temperature and polarisation) or searches for dark matter annihilation. We conclude with some remarks on the relevance to modelling of the polarised foreground.

26 pages, 12 figures; comments and references added; to appear in JCAP

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Cited by in corpus (24)

• Planck 2013 results. I. Overview of products and scientific results
• Planck 2015 results. XXV. Diffuse low-frequency Galactic foregrounds
• Polarised radio filaments outside the Galactic plane
• Fingerprints of Galactic Loop I on the Cosmic Microwave Background
• The Coherent Magnetic Field of the Milky Way
• New constraints on modelling the random magnetic field of the MW
• The Radio Synchrotron Background: Conference Summary and Report
• A global view on star formation: The GLOSTAR Galactic plane survey. II. Supernova Remnants in the first quadrant of the Milky Way
• Practical Modeling of Large-Scale Galactic Magnetic Fields: Status and Prospects
• The Parker Instability in Disk Galaxies
• The isotropic radio background revisited
• Circular polarization of the CMB: Foregrounds and detection prospects
• Planck intermediate results. XXIII. Galactic plane emission components derived from Planck with ancillary data
• Deciphering Residual Emissions: Time-Dependent Models for the Non-Thermal Interstellar Radiation from the Milky Way
• Skewness and Kurtosis as Indicators of Non-Gaussianity in Galactic Foreground Maps
• Turbulent power distribution in the local interstellar medium
• The nature of non-Gaussianity and statistical isotropy of the 408 MHz Haslam synchrotron map
• The spectral index of polarized diffuse Galactic emission between 30 and 44 GHz
• Fingerprint of Galactic Loop I on polarized microwave foregrounds
• Signatures of Recent Cosmic-Ray Acceleration in the High-Latitude $\gamma$-Ray Sky
• Footprints of Loop I on Cosmic Microwave Background Maps
• The Orion-Taurus ridge: a synchrotron radio loop at the edge of the Orion-Eridanus superbubble
• Dark Matter constraints from Planck observations of the Galactic polarized synchrotron emission
• Statistical properties of Galactic synchrotron temperature and polarization maps -- a multi-frequency comparison