Probing Cosmic Magnetic Fields Over Ten Billion Years

Details Probing Cosmic Magnetic Fields Over Ten Billion Years Probing Cosmic Magnetic Fields Over Ten Billion Years

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21348203g&link_type=abstract

American Astronomical Society, AAS Meeting #213, #482.03; Bulletin of the American Astronomical Society, Vol. 41, p.450

Astronomy and Astrophysics

Astronomy

Scientific paper

Faraday rotation is a powerful potential probe of how magnetic fields in the Universe have evolved. In particular, a statistical ensemble of extragalactic radio sources with both rotation measures (RMs) and redshifts can trace the evolution of galactic magnetic fields over cosmic time, because magnetic fields in galaxy-scale intervenors will manifest themselves as a trend in the distribution of background RMs as a function of z. Recent studies of large samples of extragalactic RMs indicate that some distant sources have very high RMs, while overall there is a deficit of very small RMs for the highest redshift sources. These effects suggest that galaxies just a few billion years old already had field strengths comparable to that seen in the Milky Way today.
Here we present new Faraday rotation observations of a large sample of extragalactic sources taken with the Australia Telescope Compact Array. This data-set doubles the sample of sources with RMs at z > 1, and also extends such studies to higher z than was previously available. We discuss the extent to which these new data confirm the dependence of RM with redshift seen in existing data. We also use these measurements to search for an evolution of galactic magnetic fields as a function of time out to z 4. These data, along with deeper upcoming surveys with the next generation of radio telescopes, can provide direct constraints on the time scale for magnetic field amplification as galaxies evolve.
B.M.G. acknowledges the support of a Federation Fellowship from the Australian Research Council through grant FF0561298. P.P.K. acknowledges support from the DOE, and from NSERC (Canada).

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