Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation

Abstract

Context. The existence of magnetic fields in the circumgalactic medium (CGM) is largely unconstrained. Their detection is important as magnetic fields can have a significant impact on the evolution of the CGM and, in turn, the fields can serve as tracers for dynamical processes in the CGM. Aims. With Faraday rotation of polarised background sources, we aim to detect a possible excess of the rotation measure in the surrounding area of nearby galaxies. Methods. We use 2,461 residual rotation measures (RRMs) observed with the LOw Frequency ARray (LOFAR), where the foreground contribution from the Milky Way is subtracted. The RRMs are then studied around a subset of 183 nearby galaxies that was selected by apparent $B$-band magnitude. Results. We find that, in general, the RRMs show no significant excess for small impact parameters (i.e. the perpendicular distance to the line of sight). However, if we only consider galaxies at higher inclination angles and sight lines that pass close to the minor axis of the galaxies, we find significant excess at impact parameters of less than 100 kpc. The excess in |RRM| is 3.7 $\mathrm{rad}{\mathrm{m}}^{-2}$ with an uncertainty between $\pm 0.9\mathrm{rad}{\mathrm{m}}^{-2}$ and $\pm 1.3\mathrm{rad}{\mathrm{m}}^{-2}$ depending on the statistical properties of the background (2.8$\sigma$-4.1$\sigma$). With electron densities of ~$10^{-4}\mathrm{c}{\mathrm{m}}^{-3}$ this suggests magnetic field strengths of a few tenths of a micro Gauss. Conclusions. Our results suggest a slow decrease of the magnetic field strength with distance from the galactic disc such as expected if the CGM is magnetised by galactic winds and outflows.

5 pages, 4 figures, accepted as Letter to Astronomy and Astrophysics

References in corpus (21)

• The Circumgalactic Medium
• HyperLEDA. III. The catalogue of extragalactic distances
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• The LOFAR Two-metre Sky Survey -- V. Second data release
• Strong magnetic fields in normal galaxies at high redshifts
• The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies
• Halo Gas Cross Sections And Covering Fractions of MgII Absorption Selected Galaxies
• Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy
• Predictions for the Angular Dependence of Gas Mass Flow Rate and Metallicity in the Circumgalactic Medium
• The dependence of cosmic ray driven galactic winds on halo mass
• CHANG-ES XXII: Coherent Magnetic Fields in the Halos of Spiral Galaxies
• Faraday Rotation from Magnesium II Absorbers towards Polarized Background Radio Sources
• Magnetic field evolution in cosmic filaments with LOFAR data
• CHANG-ES XV: Large-scale magnetic field reversals in the radio halo of NGC 4631
• Constraints on Large-Scale Magnetic Fields in the Intergalactic Medium Using Cross-Correlation Methods
• Constraining Magnetic Fields in the Circumgalactic Medium
• CHANG-ES XXI. Transport processes and the X-shaped magnetic field of NGC 4217: off-center superbubble structure
• Galactic 26Al traces metal loss through hot chimneys
• Heightened Faraday Complexity in the inner 1 kpc of the Galactic Centre
• Synthetic ${}^{26}$Al emission from galactic-scale superbubble simulations
• Magnetic fields in elliptical galaxies: Using the Laing-Garrington effect in radio galaxies and polarized emission from background radio sources

Cited by in corpus (2)

• Probing magnetic fields in the circumgalactic medium using polarization data from MIGHTEE
• Deep Synoptic Array Science: Implications of Faraday Rotation Measures of Localized Fast Radio Bursts