Probing magnetic fields in the circumgalactic medium using polarization data from MIGHTEE

¹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: Kathrin.Boeckmann@hs.uni-hamburg.de
² Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
³ Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁴ Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁵ Department of Physics and Electronics, Rhodes University, PO Box 94 Makhanda 6140, South Africa
⁶ South African Radio Astronomy Observatory, 2 Fir Street, Observatory 7925, South Africa
⁷ Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁸ National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, NM 87801, USA
⁹ Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, M13 9PL Manchester, UK
¹⁰ The Alan Turing Institute, Euston Road, London NW1 2DB, UK
¹¹ Department of Physics and Astronomy, The University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
¹² Inter-University Institute for Data Intensive Astronomy, and Department of Astronomy, University of the Western Cape, 7535 Bellville, South Africa

Received: 29 April 2023
Accepted: 29 August 2023

Abstract

Context. The properties and evolution of magnetic fields surrounding galaxies are observationally largely unconstrained. The detection and study of these magnetic fields is important to understand galaxy evolution since magnetic fields are tracers for dynamical processes in the circumgalactic medium (CGM) and can have a significant impact on the evolution of the CGM.

Aims. The Faraday rotation measure (RM) of the polarized light of background radio sources passing through the magnetized CGM of intervening galaxies can be used as a tracer for the strength and extent of magnetic fields around galaxies.

Methods. We used rotation measures observed by the MIGHTEE-POL (MeerKAT International GHz Tiered Extragalactic Exploration polarization) survey by MeerKAT in the XMM-LSS and COSMOS fields to investigate the RM around foreground star-forming galaxies. We used spectroscopic catalogs of star-forming and blue cloud galaxies to measure the RM of MIGHTEE-POL sources as a function of the impact parameter from the intervening galaxy. In addition, we examined the dependence of the RM on redshift. We then repeated this procedure using a deeper galaxy catalog with photometric redshifts.

Results. For the spectroscopic star-forming sample, we find a redshift-corrected |RM| excess of 5.6 ± 2.3 rad m⁻² which corresponds to a 2.5σ significance around galaxies with a median redshift of z = 0.46 for impact parameters below 130 kpc only selecting the intervenor with the smallest impact parameter. Making use of a photometric galaxy catalog and taking into account all intervenors with M_g < −13.6 mag, the signal disappears. We find no indication for a correlation between redshift and RM, nor do we find a connection between the total number of intervenors to the total |RM|.

Conclusions. We have presented tentative evidence that the CGM of star-forming galaxies is permeated by coherent magnetic fields within the virial radius. We conclude that mostly bright, star-forming galaxies with impact parameters less than 130 kpc significantly contribute to the RM of the background radio source.