COSMIC MAGNETIC-FIELDS IN LARGE-SCALE FILAMENTS AND SHEETS

We consider the possibility that cosmic magnetic field, instead of bei ng uniformly distributed, is strongly correlated with the large scale structure of the universe. Then, the observed rotational measure of ex tra-galactic radio sources would be caused mostly by the clumpy magnet ic field in cosmological filaments/sheets rather than by a uniform mag netic field, which was often assumed in previous studies. As a model f or the inhomogeneity of the cosmological magnetic field, we adopt a co smological hydrodynamic simulation, where the field is passively inclu ded, and can approximately represent the real field distribution with an arbitrary normalization for the field strength. Then, we derive an upper limit of the magnetic field strength by comparing the observed l imit of rotational measure with the rotational measure expected from t he magnetic field geometry in the simulated model universe. The result ing upper limit to the magnetic field in filaments and sheets is (B) o ver bar(fs) less than or similar to 1 mu G which is similar to 10(3) t imes higher than the previously quoted values. This value is close to, but larger than, the equipartition magnetic field strength in filamen ts and sheets. The amplification mechanism of the magnetic field to th e above strength is uncertain. The implications of such a strength of the cosmic magnetic field are discussed.