The Spatial Energy Spectrum of Magnetic Fields in Our Galaxy

Interstellar magnetic fields exist over a broad range of spatial scales, extending from the large Galactic scales (∼ 10 kpc) down to the very small dissipative scales (≪ 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 ≃ 10 kpc (assuming R⊙ = 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 α = −0.37± 0.10 for EB(k) = C k and an rms field strength of approximately 6μG over the relevant scales. Our study complements the derivation of the magnetic energy spectrum over the scale range 0.03 − 100 pc by Minter & Spangler (1996), showing that the magnetic spectrum becomes flatter at larger scales. This observational result is discussed in the framework of current theoretical and numerical models. Subject headings: ISM: magnetic fields — pulsars: general — turbulence