Magnetic field in early galaxies

por Dmitry Sokoloff (Moscow State Univ)

miércoles 22 abr. 2009 12:00 → 13:00 Europe/Madrid

Sala Seminarios IFIC (Edf. Institutos de Investigación)

In the context of models of galaxy formation and evolution, the cosmological evolution of large- and small-scale magnetic fields inside galaxies is discussed. We use the dynamo theory to derive the timescales of amplification and ordering of magnetic fields in disk and puffy galaxies. Turbulence in protogalactic halos generated by thermal virialization can drive an efficient turbulent dynamo. The turbulent (small-scale) dynamo was able to amplify a weak seed magnetic field in halos of protogalaxies to a few μG strength within a few 108 yr. This turbulent field served as a seed to the mean-field (large-scale) dynamo. Galaxies similar to the Milky Way formed their disks at z≈10 and regular fields of μG strength and a few kpc coherence length were generated within 2 Gyr (at z≈3), but field-ordering on the coherence scale of the galaxy size required an additional 6 Gyr (at z≈0.5). Giant galaxies formed their disks at z≈10, allowing more efficient dynamo generation of strong regular fields (with kpc coherence length) already at z≈4. However, the age of the Universe is short for fully coherent fields in giant galaxies larger than 15 kpc to have been achieved. Dwarf galaxies should have hosted fully coherent fields at z≈1. After a major merger, the strength of the turbulent field is enhanced by a factor of a few. This evolutionary scenario can be tested by measurements of polarized synchrotron emission and Faraday rotation with the planned Square Kilometre Array (SKA).