The spatial energy spectrum of magnetic fields in our Galaxy

Abstract

Interstellar magnetic fields exist over a broad range of spatial scales, extending from the large Galactic scales ($\sim 10$ kpc) down to the very small dissipative scales ($\ll 1$ pc). In this paper, we use a set of 490 pulsars distributed over roughly one third of the Galactic disk out to a radius $R\simeq 10$ kpc (assuming $R_{\odot }=8.5$ kpc) and combine their observed rotation and dispersion measures with their estimated distances to derive the spatial energy spectrum of the Galactic interstellar magnetic field over the scale range $0.5-15$ kpc. We obtain a nearly flat spectrum, with a 1D power-law index $\alpha =-0.37\pm 0.10$ for $E_{\mathrm{B}}(k)=C{k}^{\alpha }$ and an rms field strength of approximately $6\mu$G over the relevant scales. Our study complements the derivation of the magnetic energy spectrum over the scale range $0.03-100$ pc by \citet{ms96b}, showing that the magnetic spectrum becomes flatter at larger scales. This observational result is discussed in the framework of current theoretical and numerical models.

7 pages, 6 figures, ApJ accepted

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