Primordial Magnetic Fields at Cosmic Dawn: 21-cm Forecasts with HERA and SKA
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| Format: | Preprint |
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2026
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| _version_ | 1866917466572062720 |
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| author | Worku, Keduse Cruz, Hector Afonso G. Kamionkowski, Marc |
| author_facet | Worku, Keduse Cruz, Hector Afonso G. Kamionkowski, Marc |
| contents | Primordial magnetic fields (PMFs) can enhance the abundance of low-mass halos during Cosmic Dawn by sourcing additional small-scale matter fluctuations. This enhanced small-scale power can accelerate early galaxy formation, shifting the timing of Lyman-$α$ coupling, X-ray heating, and reionization toward earlier times and imprinting correlated signatures on the global and fluctuating 21-cm signals. We extend the fast analytic framework {\tt\string zeus21} to include a physically motivated PMF contribution to the linear matter power spectrum, including radiative damping before recombination and magnetic-pressure suppression below the magnetic Jeans scale. The implementation preserves the speed and modularity of {\tt\string zeus21}, enabling efficient exploration of PMF parameter space. For $n_B=-2.9$, we quantify the impact of PMFs on early structure formation and 21-cm observables across a range of fiducial magnetic amplitudes, and forecast detectability with \textit{HERA} and \textit{SKA}. Combining 21-cm forecasts with external CMB priors, we find that upcoming experiments can probe PMFs through their impact on small-scale structure, providing constraints complementary to existing cosmological probes. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_05323 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Primordial Magnetic Fields at Cosmic Dawn: 21-cm Forecasts with HERA and SKA Worku, Keduse Cruz, Hector Afonso G. Kamionkowski, Marc Cosmology and Nongalactic Astrophysics Primordial magnetic fields (PMFs) can enhance the abundance of low-mass halos during Cosmic Dawn by sourcing additional small-scale matter fluctuations. This enhanced small-scale power can accelerate early galaxy formation, shifting the timing of Lyman-$α$ coupling, X-ray heating, and reionization toward earlier times and imprinting correlated signatures on the global and fluctuating 21-cm signals. We extend the fast analytic framework {\tt\string zeus21} to include a physically motivated PMF contribution to the linear matter power spectrum, including radiative damping before recombination and magnetic-pressure suppression below the magnetic Jeans scale. The implementation preserves the speed and modularity of {\tt\string zeus21}, enabling efficient exploration of PMF parameter space. For $n_B=-2.9$, we quantify the impact of PMFs on early structure formation and 21-cm observables across a range of fiducial magnetic amplitudes, and forecast detectability with \textit{HERA} and \textit{SKA}. Combining 21-cm forecasts with external CMB priors, we find that upcoming experiments can probe PMFs through their impact on small-scale structure, providing constraints complementary to existing cosmological probes. |
| title | Primordial Magnetic Fields at Cosmic Dawn: 21-cm Forecasts with HERA and SKA |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2605.05323 |