Highly magnetized galaxies at cosmic noon shrouded in energetic cosmic ray halos

Highly magnetized galaxies at cosmic noon shrouded in energetic cosmic ray halos
by Sophie Jenkins
London, UK (SPX) Aug 13, 2025
A multinational team led by the Institute for Research in Fundamental Sciences (IPM), with contributions from the Inter-University Institute for Data-Intensive Astronomy (IDIA) and the University of Oxford, has examined 160 distant galaxies using South Africa's MeerKAT radio telescope. The study provides the first comparative measurements of their radio spectra, magnetic field intensities, and star formation rates when the universe was 9 to 12 billion years younger.

Understanding galaxy formation and evolution requires data from systems billions of light years away. While optical observations reveal that galaxies began slowing star formation after the so-called cosmic noon around 10-11 billion years ago, dust can obscure such measurements. Radio signals, unaffected by dust, offer clearer insights. This drove the team to conduct deep radio observations using MeerKAT, a precursor to the Square Kilometer Array Observatory.

Prof. Russ Taylor, co-principal investigator of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey, explained that radio wavelengths between 1 and 10 GHz are particularly reliable for gauging star formation rates. Building on earlier work with nearby galaxies, lead researcher Prof. Fatemeh Tabatabaei used MIGHTEE and other surveys to extend the analysis to galaxies at cosmic noon and earlier epochs.

Dr. Maryam Khademi of IPM noted that the radio spectrum in these early galaxies changes with their star formation rate, revealing new details about their evolution. The emission is dominated by synchrotron radiation from high-energy cosmic rays spiraling along magnetic fields. In galaxies with stronger fields and higher star formation, cosmic rays appear to gain more energy than expected.

The findings suggest that cosmic rays may be energized through magnetic mirrors or detached from magnetic fields by galactic winds and outflows. Prof. Tabatabaei added that highly tangled and turbulent magnetic fields can accelerate these particles, which then scatter away, forming large halos of energetic cosmic rays. This mechanism also accounts for the excess radio output compared to infrared emissions observed in the sample.

Research Report:The Radio Spectral Energy Distribution and Star Formation Calibration in MIGHTEE-COSMOS Highly Star-forming Galaxies at 1.5 < z < 3.5