Kavli Affiliate: Susan Clark
| Summary:
We present a distance-resolved reconstruction of the local line-of-sight Galactic magnetic field, $B_$, by combining a 3D electron density ($n_e$) map derived from dust map-informed simulations and a full-sky map of Faraday rotation measure (RM). The forward model evaluates RM on the same 3D grid as the $n_e$ map and compares to the Galactic Faraday rotation sky. We infer $B_$ with a Gaussian-process prior whose power spectrum is inferred from the data using geometric variational inference. The result is a local (within 1.25 kpc where $|b|>5^circ$) map of $B_$ with uncertainties. The reconstructed RM sky reproduces prominent features of Faraday rotation sky, with a root mean square average strength of $B_$ of $1.63pm 0.16$ $μ$G. In face-on views, the magnetic field exhibits coherent patches with alternating sign and hints of kpc-scale modulations, but with significant structure seen on scales of order 100 pc. The $B_$ field is seen to exhibit a 3D power spectrum with an average slope of $-2.73 pm 0.19$. We validate our $B_$ reconstruction with Galactic pulsars. Predicted RMs (computed by integrating $n_eB_$ to each pulsar’s distance) correlates with observed RMs, and predicted dispersion measures (DMs) from the $n_e$ map also correlate with measured DMs, albeit with significant scatter.
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