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Delayed Recombination

P. J. E. Peebles, Sara Seager, Wayne Hu

TL;DR

The paper investigates whether early Ly-alpha photon sources at $z\sim1000$ can delay recombination and bias CMB-based inferences of spatial curvature. A simple homogeneous Ly-alpha source model with $\frac{dn_\alpha}{dt} = \epsilon_\alpha n_H H(t)$ shows that a delay can modestly shift the first peak and suppress secondary peaks while keeping post-recombination Thomson optical depth small. The pattern of higher acoustic peaks, especially the suppression of the second peak described by $A_2(\epsilon_\alpha) \approx A_2(0) \frac{z_*(\epsilon_\alpha)}{z_*(0)}$, can distinguish delayed recombination from curvature or baryon density changes. Measurements of the third peak and the full peak structure are crucial to test this scenario.

Abstract

Under the standard model for recombination of the primeval plasma, and the cold dark matter model for structure formation, recent measurements of the first peak in the angular power spectrum of the cosmic microwave background temperature indicate the spatial geometry of the universe is nearly flat. If sources of Lya resonance radiation, such as stars or active galactic nuclei, were present at z ~ 1000 they would delay recombination, shifting the first peak to larger angular scales, and producing a positive bias in this measure of space curvature. It can be distinguished from space curvature by its suppression of the secondary peaks in the spectrum.

Delayed Recombination

TL;DR

The paper investigates whether early Ly-alpha photon sources at can delay recombination and bias CMB-based inferences of spatial curvature. A simple homogeneous Ly-alpha source model with shows that a delay can modestly shift the first peak and suppress secondary peaks while keeping post-recombination Thomson optical depth small. The pattern of higher acoustic peaks, especially the suppression of the second peak described by , can distinguish delayed recombination from curvature or baryon density changes. Measurements of the third peak and the full peak structure are crucial to test this scenario.

Abstract

Under the standard model for recombination of the primeval plasma, and the cold dark matter model for structure formation, recent measurements of the first peak in the angular power spectrum of the cosmic microwave background temperature indicate the spatial geometry of the universe is nearly flat. If sources of Lya resonance radiation, such as stars or active galactic nuclei, were present at z ~ 1000 they would delay recombination, shifting the first peak to larger angular scales, and producing a positive bias in this measure of space curvature. It can be distinguished from space curvature by its suppression of the secondary peaks in the spectrum.

Paper Structure

This paper contains 4 sections, 10 equations, 4 figures.

Table of Contents

  1. Introduction
  2. The Model
  3. Temperature Anisotropy Power Spectrum
  4. Discussion

Figures (4)

  • Figure 1: The ionization fraction, $x$, as a function of redshift for $\epsilon_{i}=0$ and various values of $\epsilon_{\alpha}$.
  • Figure 2: The effect of new sources of ionizing photons on the recombination history. For each value of $\epsilon_{\rm i}$ the upper curve is for $\epsilon_{\alpha}=1$ and the lower curve for $\epsilon_{\alpha}=0$.
  • Figure 3: The temperature anisotropy power spectrum ($\Delta T = [\ell(\ell+1)C_{\ell}/2\pi]^{1/2}$) for various values of the Ly $\alpha$ production parameter $\epsilon_{\alpha}$.
  • Figure 4: A delay in recombination (with $\epsilon_{\alpha}=1000$) can make an open universe ($\Omega_m=0.6$, dashed line) appear flat (solid line, $\Omega_m=0.25$, $\Omega_\Lambda$=0.75) or decrease $\ell_1$ in a flat universe and suppress the secondary peaks (with $\epsilon_{\alpha}=10$). The COBE and BOOMERanG data are plotted as bandwidth $\times 1\sigma$ error boxes.