Latest Results Archives - GUAIX GROUP

LoTSS DR3 RM Grid: Upcoming Release

Shane O'Sullivan — Thu, 16 Apr 2026 14:49:39 +0000

The forthcoming DR3 RM Grid will provide rotation measures and host identifications for over 5000 sources, significantly expanding low-frequency studies of cosmic magnetism. Description paper (O’Sullivan et al. 2026) and data product links coming soon.

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RM Grids with the Square Kilometre Array (SKA)

Shane O'Sullivan — Thu, 16 Apr 2026 14:46:16 +0000

We have developed predictions for next-generation metre-wavelength RM grids with SKA-Low, showing that it will deliver a step change in sensitivity and source density for studies of cosmic magnetism. SKA-Low is expected to provide an order-of-magnitude improvement over current low-frequency RM grids (ie. the LOFAR RM Grid), with source densities of several RMs per square degree and with exceptional RM precision. These advances will enable precision constraints on the origin and evolution of cosmic magnetic fields, from galaxy halos to the cosmic web.

RM Grid predictions for SKA-Low: O’Sullivan et al. (2026), Advancing Astrophysics with the SKA – II, AASKAII/53, in press

Cumulative polarized-source number counts: updated T-RECS polarization (blue), LOFAR deep field polarized source counts from Piras et al. (2024) (red), LoTSS DR2 RM Grid counts (green), power- law fit to model between 0.1 and 10 mJy (orange).

We have also implemented direction-dependent Faraday synthesis within DDFacet in Gustaffson et al. (2025), enabling more accurate wide-field polarimetric imaging by jointly reconstructing sky position and Faraday depth while correcting for instrumental and ionospheric effects. Applied to SKA data, this approach will improve polarized source recovery, reduce imaging artefacts, and enable deeper, higher-fidelity RM surveys across wide fields, particularly for faint and complex polarized sources.

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Magnetic Fields in the Shapley Supercluster Core (Alonso-López et al. 2026)

Shane O'Sullivan — Thu, 16 Apr 2026 14:32:05 +0000

Using a dense POSSUM RM grid together with Planck thermal SZ data, we probed the magnetised gas in the core of the Shapley Supercluster, one of the densest structures in the local Universe. We detected a clear excess in RM scatter across the region, indicating magnetic field strengths of roughly 1–3 μG in the clusters and groups. Comparing the observations with semi-analytic models and cosmological MHD simulations revealed flatter-than-expected RM profiles in the cluster outskirts, highlighting a tension with current models of magnetic field amplification. These results show that wide-area RM grids can directly trace magnetised gas beyond cluster cores and into the interacting supercluster environment. See Alonso-López, O’Sullivan et al. (2026) for details.

RM scatter profile as a function of distance to the nearest cluster. The black line shows the observed trend, with the grey shaded region indicating the 68% confidence interval from bootstrap resampling. The coloured bands show the results from cosmological MHD simulations for different magnetic-field amplification models in the intercluster region.

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