Speaker
Description
Magnetic fields are ubiquitous in galaxies and play a fundamental role in their dynamics and evolution. However, observational constraints on magnetic fields in the Circumgalactic Medium (CGM), particularly at intermediate to high z, remain limited. In this work, we investigate CGM magnetisation using a large sample of quasar Rotation Measures (RMs) from ASKAP, statistically separating sightlines that intersect foreground galaxies identified via Mg II absorption from control samples. After carefully mitigating Galactic foreground contributions, we detect a significant excess in the residual RM dispersion of 4.13 ∓ 0.91 rad m^-2 associated with intervening galaxies. This excess indicates the presence of coherent magnetic fields in galaxy halos, with strengths of 0.4 - 0.8 𝜇G over projected radii of 20-150 kpc, suggesting that substantial CGM magnetisation was already in place by z∼1.
These results provide constraints on the origin and amplification of magnetic fields in the CGM over cosmic time. In this context, upcoming facilities like AtLAST will play a transformative role. Through dust polarisation measurements, AtLAST will enable complementary probes of magnetic fields in the ISM and CGM in dusty, high-z systems, inaccessible to traditional RM-based techniques. The synergy between Faraday rotation studies and dust polarisation observations offers a powerful pathway to build a comprehensive, multi-scale picture of extragalactic magnetic fields across cosmic epochs.