Abstract
We reconstruct for the first time the three dimensional structure of magnetic fields on cosmological scales, which were seeded by density perturbations during the radiation dominated epoch of the Universe and later on were evolved by structure formation. To achieve this goal, we rely on three dimensional initial density fields inferred from the 2M++ galaxy compilation via the Bayesian BORG algorithm. Using those, we estimate the magnetogenesis by the so called Harrison mechanism. This effect produced magnetic fields exploiting the different photon drag on electrons and ions in vortical motions, which are exited due to second order perturbation effects in the Early Universe. Subsequently we study the evolution of these seed fields through the non-linear cosmic structure formation by virtue of a magneto-hydrodynamics simulation to obtain a 3D estimate for the structure of this primordial magnetic field component today. At recombination we obtain large scale magnetic field strengths around , with a power spectrum peaking at about in comoving scales. At present we expect this evolved primordial field to have strengths above ≈10 and ≈10 in clusters of galaxies and voids, respectively. We also calculate the corresponding Faraday rotation measure map and show the magnetic field morphology and strength for specific objects of the Local Universe. These results provide a reliable lower limit on the primordial component of the magnetic fields in these structures.
Highlights
Inference of primordial magnetic fields opens a unique window into the Early Universe between inflation and recombination
We apply adaptive mesh refinement (AMR) only in the innermost (120 Mpc h−1)3 region of the simulation, centred on the Milky Way location, and allowed for 5 levels of refinement whenever the local gas/dark matter density exceeded the mean density of surrounding cells by a factor of 3; the procedure is recursively repeated at each AMR level
We used our knowledge about the large scale structure in the Universe coming from the 2M++ galaxy survey and the BORG algorithm to infer the corresponding density distributions deep in the radiation epoch
Summary
Inference of primordial magnetic fields opens a unique window into the Early Universe between inflation and recombination. The recent progress on the inference of the actual 3D realization of the large-scale dark matter structure and its formation history in the Local Universe and the fact that the Harrison mechanism is solely founded on well established plasma physics allows us to calculate the seed magnetic fields that had to be generated by this effect as well as their present day morphology and strength. Since these fields have to exist today in combination with fields of other sources, we are able to provide credible lower bounds on the primordial magnetic field strength in the nearby Universe.
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