Probing the magneto-ionic medium of the Milky Way using pulsars

Saakshi Dhakal; Amit Seta

doi:10.1093/mnras/staf1816

paper

Probing the magneto-ionic medium of the Milky Way using pulsars

arXiv:2510.12991 · doi:10.1093/mnras/staf1816

Abstract

Magnetic fields are fundamental to the dynamics of the interstellar medium (ISM) in spiral galaxies and are often separated into large-scale, regular ( $B$ ) and small-scale, random ( $b$ ) components. The thermal electron density, $n_{e}$ , can also be divided into large-scale, diffuse, $⟨ n_{e} ⟩$ , and small-scale, clumpy, $δ n_{e}$ , components. Estimating the properties of $b$ and $δ n_{e}$ from observations, even within the Milky Way, has long been challenging. This work addresses the challenge using pulsars, which probe the Milky Way's magneto-ionic medium. Using data of more than 1200 pulsars from the Australia Telescope National Facility pulsar catalogue, we combine dispersion ( $DM$ ) and rotation ( $RM$ ) measures with theoretical models to estimate both small- and large-scale properties of the Galactic magnetic field and thermal electron density. We find no significant correlation between the average parallel magnetic field strength, $⟨ B_{∥} ⟩ [μ G] = 1.232 RM [rad m^{- 2}] / DM [pc c m^{- 3}]$ , and pulsar distance. For pulsars within $20 kpc$ , we estimate $∣ B ∣ \approx 1.2 μ G$ and $⟨ n_{e} ⟩ \approx 0.05 cm^{- 3}$ . More importantly, we determine correlation lengths of small-scale components, $ℓ_{b} \approx 20$ -- $30 pc$ and $ℓ_{δ n_{e}} \approx 250$ -- $300 pc$ . At smaller distances, $B$ remains roughly constant, while $⟨ n_{e} ⟩$ increases and both length scales decrease. These results refine our understanding of fundamental scales in the magneto-ionic medium, aiding the interpretation of extragalactic $RM$ s and providing insights into the role of magnetic fields in galaxies.

16 pages, 6 figures, accepted in MNRAS

Probing the magneto-ionic medium of the Milky Way using pulsars

Abstract

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