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Constraints on primordial magnetic fields from high redshift quasars

Presentation #316.07 in the session AGN and Quasars V.

Published onJun 29, 2022
Constraints on primordial magnetic fields from high redshift quasars

Magnetic fields are known to permeate galaxies, yet their origin is unclear. A likely explanation is that magnetic fields grow from a seed field through a dynamo, where the seed field is either a relic of inflation or due to turbulence in the interstellar medium during structure formation. Optical emission lines in the spectra of luminous quasars provide a window into physical conditions, such as magnetic fields and shock velocities, in the regions surrounding supermassive black holes. At early cosmic times which provide the strongest constraints on seed fields, the characterization of these conditions is a challenge since key diagnostics emission lines are redshifted in the observed near/mid-infrared wavelengths. In this study, we show for the first time, that typical indicated magnetic field strengths in distant quasars at z~5.9 exceed 6 μG. This is similar to that estimated for some of the most luminous active galactic nuclei in the local Universe. Our measurement implies that strong, coherent magnetic fields were present in the interstellar medium at a time when the universe was < 1 billion years old. Comparing our estimated magnetic field strengths with models for the evolution of galaxy-scale fields, favors high seed field strengths exceeding 0.3μG, the first observational constraint on such fields. This high value favors scenarios where seed magnetic fields were produced by turbulence in the early stages of galaxy formation.

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