CMB anisotropy due to tangled magnetic fields in reionized models

Abstract

Primordial tangled cosmological Magnetic Fields source rotational velocity perturbations of the baryon fluid, even in the post-recombination universe. These vortical modes inturn leave a characteristic imprint on the temperature anisotropy of the Cosmic Microwave Background (CMB), if the CMB photons can be rescattered after recombination. Observations from WMAP indicate that the Universe underwent a relatively early reionization (z_ri∼15), which does indeed lead to a significant optical depth for rescattering of CMB photons after the reionization epoch. We compute the resulting additional temperature anisotropies, induced by primordial magnetic fields in the post-recombination universe. We show that in models with early reionization, a nearly scale-invariant spectrum of tangled magnetic fields which redshift to a present value of B₀∼3×10^-9 Gauss, produce vector mode perturbations which in turn induce additional temperature anisotropy of about 0.3 to 0.4 μK over very small angular scales, with l upto ∼10000 or so.