New algorithm separates galaxy's magnetic fingerprint from deep-space signals

Mapping magnetic fields in large-scale cosmic structure requires peeling apart overlapping Faraday rotation signals — one from the Milky Way, one from extragalactic space — mixed together in every radio polarization measurement. The DEFROST algorithm takes rotation-measure catalogs plus redshift data and disentangles these contributions while properly accounting for observing noise. Tests on synthetic data show the method recovers extragalactic parameters within 5-sigma accuracy for sources above 45 degrees Galactic latitude, across a realistic range of noise levels and source densities. The results set concrete guidelines for using current and forthcoming radio surveys to probe weak magnetic fields in the cosmic web.