Probing small-scale cosmological fluctuations with the 21 cm forest: effects of neutrino mass, running spectral index and warm dark matter

Abstract

Although the cosmological paradigm based on cold dark matter and adiabatic, nearly scale-invariant primordial fluctuations is consistent with a wide variety of existing observations, it has yet to be sufficiently tested on scales smaller than those of massive galaxies, and various alternatives have been proposed that differ significantly in the consequent small-scale power spectrum (SSPS) of large-scale structure. Here we show that a powerful probe of the SSPS at $k\gtrsim 10$ Mpc${}^{-1}$ can be provided by the 21 cm forest, that is, systems of narrow absorption lines due to intervening, cold neutral hydrogen in the spectra of high-redshift background radio sources in the cosmic reionization epoch. Such features are expected to be caused predominantly by collapsed gas in starless minihalos, whose mass function can be very sensitive to the SSPS. As specific examples, we consider the effects of neutrino mass, running spectral index (RSI) and warm dark matter (WDM) on the SSPS, and evaluate the expected distribution in optical depth of 21 cm absorbers out to different redshifts. Within the current constraints on quantities such as the sum of neutrino masses $\sum m_{\nu }$, running of the primordial spectral index $d{n}_s/d\ln k$ and WDM particle mass $m_{\mathrm{WDM}}$, the statistics of the 21 cm forest manifest observationally significant differences that become larger at higher redshifts. In particular, it may be possible to probe the range of $m_{\mathrm{WDM}}\gtrsim 10$ keV that may otherwise be inaccessible. Future observations of the 21 cm forest by the Square Kilometer Array may offer a unique and valuable probe of the SSPS, as long as radio sources such as quasars or Population III gamma-ray bursts with sufficient brightness and number exist at redshifts of $z\gtrsim$ 10 - 20, and the astrophysical effects of reionization and heating can be discriminated.

12pages, 11 figures, accepted for publication in PRD

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• Probing the primordial Universe with 21-cm line from cosmic dawn/epoch of reionization
• 21cm forest probes on the axion dark matter in the post-inflationary Peccei-Quinn symmetry breaking scenarios
• Radiative Corrections from Heavy Fast-Roll Fields during Inflation
• Deep learning-driven likelihood-free parameter inference for 21-cm forest observations
• Prospects for Observing High-redshift Radio-loud Quasars in the SKA Era: Paving the Way for 21-cm Forest Observations
• Analyzing the 21cm forest with Wavelet Scattering Transform: Insight into non-Gaussian features of the 21cm forest
• Impact of the primordial fluctuation power spectrum on the reionization history
• Prospects of a statistical detection of the 21-cm forest and its potential to constrain the thermal state of the neutral IGM during reionization
• Boosting the 21 cm forest signals by the clumpy substructures
• Impact of dark matter-baryon relative velocity on the 21cm forest
• Prospects for measuring neutrino mass with 21-cm forest
• Survival of Gas in Subhalos and Its Impact on the 21 cm Forest Signals: Insights from Hydrodynamic Simulations
• Analytical modeling of the one-dimensional power spectrum of 21-cm forest based on a halo model method
• Cosmological free-free emission from dark matter halos in the $\Lambda$CDM model
• Probing power spectrum enhancement at small scales with the SKA
• Efficient neutral-IGM inference from noisy 21-cm forest spectra with latent-space U-Net encoding and XGBoost
• Configuration Requirements for 21-cm Forest Background Quasar Searches with the Moon-based Interferometer