21cm fluctuations from primordial magnetic fields

Abstract

Recent observations of magnetic fields in intergalactic void regions and in high redshift galaxies may indicate that large scale magnetic fields have a primordial origin. If primordial magnetic fields were present soon after the recombination epoch, they would have induced density fluctuations on the one hand and dissipated their energy into the primordial gas on the other, and thereby significantly alter the thermal history of the Universe. Here we consider both the effects and calculate the brightness temperature fluctuations of the 21cm line using simple Monte Carlo simulations. We find that the fluctuations of the 21cm line from the energy dissipation appear only on very small scales and those from the density fluctuations always dominate on observationally relevant angular scales.