Abstract
In the present universe, magnetic fields exist with various strengths and on various scales. One possible origin of these cosmic magnetic fields is the primordial magnetic fields (PMFs) generated in the early universe. PMFs are considered to contribute to matter density evolution via Lorentz force and the thermal history of intergalactic medium (IGM) gas due to ambipolar diffusion. Therefore, information about PMFs should be included in the temperature anisotropy of the Cosmic Microwave Background through the thermal Sunyaev–Zel’dovich (tSZ) effect in IGM. In this article, given an initial power spectrum of PMFs, we show the spatial fluctuation of mass density and temperature of the IGM and tSZ angular power spectrum created by the PMFs. Finally, we find that the tSZ angular power spectrum induced by PMFs becomes significant on small scales, even with PMFs below the observational upper limit. Therefore, we conclude that the measurement of tSZ anisotropy on small scales will provide the most stringent constraint on PMFs.
Highlights
According to many astronomical observations, we can find the magnetic fields in the universe on a very wide range of spatial scales
We study the thermal Sunyaev–Zel’dovich (tSZ) effect induced by primordial magnetic fields (PMFs) in the case of Bn = 0.5 nG and n B = −1, which are not excluded from the Planck constraint on PMFs [11]
We have obtained a tSZ signal with a similar shape, but we have found that the signal amplitude is determined by the cut-off length of the PMFs, which depends on the values of Bn and n B
Summary
According to many astronomical observations, we can find the magnetic fields in the universe on a very wide range of spatial scales. Some papers have suggested the existence of magnetic fields in the intergalactic region, known as the cosmic voids, based on the blazars’ γ-ray observations [4,5,6,7]. The origin of these cosmic magnetic fields is an open question, especially on large scales. The first one indicates the mechanisms taking place in the primordial universe, and this scenario predicts tiny magnetic fields on cosmological scales. These weak seed fields are called “primordial magnetic fields” (PMFs). We conclude that the measurement of tSZ anisotropy on small scales will provide the most stringent constraint on PMFs.
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