Primordial Magnetic Fields at Cosmic Dawn: 21-cm Forecasts with HERA and SKA

TL;DR

This paper models how primordial magnetic fields influence early universe structure formation and 21-cm signals, forecasting detectability with upcoming radio telescopes like HERA and SKA.

Contribution

It extends the zeus21 framework to include primordial magnetic fields, enabling efficient exploration of their effects on early cosmic signals.

Findings

PMFs can significantly alter the timing of key cosmic dawn events.

Upcoming 21-cm observations can constrain PMF parameters.

The extended model remains fast and modular for broad parameter exploration.

Abstract

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-$\alpha$ 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.