scholarly journals Model-independent constraints on the hydrogen-ionizing emissivity at z > 6

2019 ◽  
Vol 489 (2) ◽  
pp. 2669-2676 ◽  
Author(s):  
Charlotte A Mason ◽  
Rohan P Naidu ◽  
Sandro Tacchella ◽  
Joel Leja

ABSTRACT Modelling reionization often requires significant assumptions about the properties of ionizing sources. Here, we infer the total output of hydrogen-ionizing photons (the ionizing emissivity, $\dot{N}_\textrm {ion}$) at z = 4–14 from current reionization constraints, being maximally agnostic to the properties of ionizing sources. We use a Bayesian analysis to fit for a non-parametric form of $\dot{N}_\textrm {ion}$, allowing us to flexibly explore the entire prior volume. We infer a declining $\dot{N}_\textrm {ion}$ with redshift at z > 6, which can be used as a benchmark for reionization models. Model-independent reionization constraints from the cosmic microwave background (CMB) optical depth and Ly α and Ly β forest dark pixel fraction produce $\dot{N}_\textrm {ion}$ evolution ($\mathrm{ d}\log _{10}\dot{\mathbf {N}}_{\bf ion}/\mathrm{ d}z|_{z=6\rightarrow 8} = -0.31\pm 0.35$ dex) consistent with the declining UV luminosity density of galaxies, assuming constant ionizing photon escape fraction and efficiency. Including measurements from Ly α damping of galaxies and quasars produces a more rapid decline: $\mathrm{ d}\log _{10}\dot{\mathbf {N}}_{\bf ion}/\mathrm{ d}z|_{z=6\rightarrow 8} =-0.44\pm 0.22$ dex, steeper than the declining galaxy luminosity density (if extrapolated beyond $M_\rm{\small UV}\gtrsim -13$), and constrains the mid-point of reionization to z = 6.93 ± 0.14.

2009 ◽  
Vol 102 (13) ◽  
Author(s):  
C. Räth ◽  
G. E. Morfill ◽  
G. Rossmanith ◽  
A. J. Banday ◽  
K. M. Górski

Author(s):  
Abraham Loeb ◽  
Steven R. Furlanetto

This chapter describes how the 21-cm line is used to study the high-z Universe. It introduces the spin-flip or the hyperfine line—a transition driven by the interaction of the spins of the proton and electron, whose relative directions affect the energy of the electron's orbit. An atom in the upper state eventually undergoes a spin-flip transition, emitting a photon with a wavelength of 21 cm. As the chapter shows, this transition is extremely weak, so the effective intergalactic medium (IGM) optical depth is only of the order of 1 percent: this makes the entire neutral IGM accessible during the cosmic dawn. Moreover, the transition energy is so low that it provides a sensitive thermometer of the low-temperature IGM, and as a low-frequency radio transition, it can be seen across the entirety of the IGM against the cosmic microwave background.


2010 ◽  
Vol 2010 ◽  
pp. 1-25 ◽  
Author(s):  
L. Raul Abramo ◽  
Thiago S. Pereira

We review the basic hypotheses which motivate the statistical framework used to analyze the cosmic microwave background, and how that framework can be enlarged as we relax those hypotheses. In particular, we try to separate as much as possible the questions of gaussianity, homogeneity, and isotropy from each other. We focus both on isotropic estimators of nongaussianity as well as statistically anisotropic estimators of gaussianity, giving particular emphasis on their signatures and the enhanced “cosmic variances” that become increasingly important as our putative Universe becomes less symmetric. After reviewing the formalism behind some simple model-independent tests, we discuss how these tests can be applied to CMB data when searching for large-scale “anomalies”.


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