An SKA-Low RM Grid for constraining the origin of cosmic magnetism
Abstract
Understanding the origin and evolution of cosmic magnetic fields is a key science goal for the SKAO. Recent advances in metre-wavelength (m-λ) Faraday rotation measure (RM) grids are enabling precision probes of cosmic magnetism, with implications extending to early-Universe physics, AGN feedback, and the magnetized circumgalactic medium. Here we model the m-λ polarized source counts to predict an RM Grid density with SKA-Low of $N(>P) \sim 5 ({P}/{100{\rm μJy}})^{-0.75}\,\, {\rm deg}^{-2} $, where P is the polarized intensity detection threshold. This represents at least an order of magnitude improvement over the current state-of-the-art. For a representative wide-area SKA-Low AA4 survey covering 10,000 deg2 in ∼3,200 hours, we predict more than 50,000 RMs. Coupled with an expected RM precision of ∼0.05 rad/m2, SKA-Low promises to produce the leading RM Grid survey for constraining the origin of cosmic magnetism in the SKA era. These predictions can be partially tested during the Science Verification phase using the AA* Sky Model data. For example, at a nominal detection threshold of 240~μJy/beam (8 times the noise in Stokes Q and U), we expect ∼2.6 RMs/deg2 (5x the current best m-λ RM Grid density). Combining both wide-area and all-sky data, SKA-Low could detect up to 100,000 m-λ RMs across its observable sky. Finally, we demonstrate new constraints on the origin of cosmic magnetism by comparing cosmological MHD simulations with the LOFAR m-λ RMs, and highlight the transformative advances an SKA-Low RM Grid will enable for precision studies of cosmic magnetism.
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BibTeX
@misc{osullivan2026skalow,
title = {{An SKA-Low RM Grid for constraining the origin of cosmic magnetism}},
author = {Shane P. O'Sullivan and Franco Vazza and Ettore Carretti and Valentina Vacca and Francesca Loi},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2606.25096},
eprint = {2606.25096},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.25096},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - An SKA-Low RM Grid for constraining the origin of cosmic magnetism
AU - Shane P. O'Sullivan
AU - Franco Vazza
AU - Ettore Carretti
AU - Valentina Vacca
AU - Francesca Loi
PY - 2026
DA - 2026/08/30
PB - arXiv
DO - 10.48550/arxiv.2606.25096
UR - https://arxiv.org/abs/2606.25096
AB - Understanding the origin and evolution of cosmic magnetic fields is a key science goal for the SKAO. Recent advances in metre-wavelength (m-λ) Faraday rotation measure (RM) grids are enabling precision probes of cosmic magnetism, with implications extending to early-Universe physics, AGN feedback, and the magnetized circumgalactic medium. Here we model the m-λ polarized source counts to predict an RM Grid density with SKA-Low of $N(>P) \sim 5 ({P}/{100{\rm μJy}})^{-0.75}\,\, {\rm deg}^{-2} $, where P is the polarized intensity detection threshold. This represents at least an order of magnitude improvement over the current state-of-the-art. For a representative wide-area SKA-Low AA4 survey covering 10,000 deg^2 in ∼3,200 hours, we predict more than 50,000 RMs. Coupled with an expected RM precision of ∼0.05 rad/m^2, SKA-Low promises to produce the leading RM Grid survey for constraining the origin of cosmic magnetism in the SKA era. These predictions can be partially tested during the Science Verification phase using the AA* Sky Model data. For example, at a nominal detection threshold of 240~μJy/beam (8 times the noise in Stokes Q and U), we expect ∼2.6 RMs/deg^2 (5x the current best m-λ RM Grid density). Combining both wide-area and all-sky data, SKA-Low could detect up to 100,000 m-λ RMs across its observable sky. Finally, we demonstrate new constraints on the origin of cosmic magnetism by comparing cosmological MHD simulations with the LOFAR m-λ RMs, and highlight the transformative advances an SKA-Low RM Grid will enable for precision studies of cosmic magnetism.
ER -