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Constraints on Features in the Cosmological Power Spectrum from Observations of the Epoch of Reionization

O. R. Skorikov, S. V. Pilipenko, M. V. Tkachev

TL;DR

This study investigates whether small-scale distortions in the primordial power spectrum, in the form of a bump or tilt, can be constrained by the epoch of reionization. Using $5$ Mpc$/h$ N-body simulations with distorted spectra and the GRUMPY semi-analytic model coupled to BPASS stellar synthesis, it computes the Lyman-continuum photon production and compares it to the ionization requirement from Madau et al., while marginalizing over uncertain $f_{esc}$ and clumping factor $C$. For a moderate bump amplitude $\mathcal{A}$ in the range $\sim 1.5$–$2$, reionization by $z\approx 8$ remains consistent with observations; only the bump centered at $k_0\approx 4.7$ Mpc$^{-1}$ can approach earlier ionization, and that too depends sensitively on $f_{esc}$ and $C$. Tilts and bumps at higher $k_0$ can yield substantial high-redshift UV photon production (up to $\sim$ orders of magnitude) but typically do not fully ionize the universe, suggesting limited constraining power from reionization z\simeq 8 data alone; future 21 cm measurements may provide stronger limits. The work links small-scale power-spectrum distortions to high-redshift ionizing photon budgets, highlighting the role of astrophysical uncertainties in interpreting early-universe constraints.

Abstract

We consider cosmological models with a power spectrum of perturbations featuring an enhanced amplitude on dwarf galaxy scales (with a "bump" or a "tilt"). Early formation of a large number of galaxies in such models, compared to the standard spectrum, can shift the epoch of reionization to higher redshifts compared to observations. We show that for moderate bump amplitude $\mathcal{A}<1.5-2$, the considered models are not ruled out by observations of reionization at $z \approx 8$ due to existing uncertainties in the fraction of ultraviolet photons escaping galaxies, $f_{esc}$, and inhomogeneity of the neutral hydrogen distribution.

Constraints on Features in the Cosmological Power Spectrum from Observations of the Epoch of Reionization

TL;DR

This study investigates whether small-scale distortions in the primordial power spectrum, in the form of a bump or tilt, can be constrained by the epoch of reionization. Using Mpc N-body simulations with distorted spectra and the GRUMPY semi-analytic model coupled to BPASS stellar synthesis, it computes the Lyman-continuum photon production and compares it to the ionization requirement from Madau et al., while marginalizing over uncertain and clumping factor . For a moderate bump amplitude in the range –, reionization by remains consistent with observations; only the bump centered at Mpc can approach earlier ionization, and that too depends sensitively on and . Tilts and bumps at higher can yield substantial high-redshift UV photon production (up to orders of magnitude) but typically do not fully ionize the universe, suggesting limited constraining power from reionization z\simeq 8 data alone; future 21 cm measurements may provide stronger limits. The work links small-scale power-spectrum distortions to high-redshift ionizing photon budgets, highlighting the role of astrophysical uncertainties in interpreting early-universe constraints.

Abstract

We consider cosmological models with a power spectrum of perturbations featuring an enhanced amplitude on dwarf galaxy scales (with a "bump" or a "tilt"). Early formation of a large number of galaxies in such models, compared to the standard spectrum, can shift the epoch of reionization to higher redshifts compared to observations. We show that for moderate bump amplitude , the considered models are not ruled out by observations of reionization at due to existing uncertainties in the fraction of ultraviolet photons escaping galaxies, , and inhomogeneity of the neutral hydrogen distribution.

Paper Structure

This paper contains 4 sections, 4 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Models and Assumptions
  3. Results
  4. Conclusion

Figures (2)

  • Figure 1: UV photon emission rate. The shaded region shows the photon number required for full ionization for clumping factor $C=3-10$.
  • Figure 2: Shaded areas show the range of UV photon emission rates in each distorted spectrum model for escape fractions $f_{esc} = 0.02 - 0.2$. The filled region shows the required photon number for full ionization for clumping factors $C=3-10$. The intersection determines the possible redshift range of reionization.