Probing power spectrum enhancement at small scales with the SKA

TL;DR

This paper explores how small-scale power spectrum enhancements affect reionization and the 21 cm signal, with implications for SKA observations.

Contribution

It demonstrates that small-scale power spectrum boosts can significantly alter the 21 cm signal, aiding future detection efforts.

Findings

21 cm power spectrum differs notably from standard models under small-scale enhancements.

SKA-low AA* telescope can potentially detect these small-scale power spectrum effects.

Even with observational constraints, the impact on ionization morphology remains significant.

Abstract

The reionization process is driven by ionizing photons from dwarf galaxies in halos with virial temperature $T_{\rm vir} \gtrsim 10^4$ K, while minihalos whose $T_{\rm vir}\lesssim 10^4$ K consume ionizing photons and have negative contributions to reionization. Since ionizing sources and minihalos have different clustering characteristics, not only the reionization history, but also the morphology of the ionization field, is sensitive to the small-scale power spectrum. If the power spectrum at small scales is enhanced compared with the standard six-parameter $\Lambda$CDM model, then both the sources and sinks of ionizing photons would be boosted and the net impact depends on the competition between them. Therefore, the 21 cm signal that can probe the morphology of the ionization field will be a useful tool for detecting the small-scale power spectrum. Using the power spectrum proposed by Cielo et al. (2025) (C25) as a demonstration, we investigate the influence of small-scale power spectrum enhancement on the ionization field and the 21 cm signal. We find that for the C25 model, even under the constraints of observed UV luminosity functions for high-$z$ galaxies and reionization history, the 21~cm power spectrum and the bubble size distribution could be still significantly different from the regular $\Lambda$CDM model. The upcoming SKA-low AA* telescope, and a further imaging telescope, have the potential to detect the small-scale power spectrum more deeply.