Primordial helium recombination. I. Feedback, line transfer, and continuum opacity

Switzer, Eric R.; Hirata, Christopher M.

doi:10.1103/physrevd.77.083006

Cited by 86 publications

(64 citation statements)

References 82 publications

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“…The presence of metals can therefore speed up hydrogen recombination by increasing the net rate of Lyman-decays. A similar process was investigated for primordial helium recombination [24,25]: in that case the presence of neutral hydrogen leads to continuum opacity in the He I 2 1 P o À 1 1 S line. To estimate the impact of continuum opacity on the Lyman-line, we use the analytic treatment presented for He I recombination in Ref.…”

Section: Effect Of Neutral Metals On the Lyman-decay Ratementioning

confidence: 95%

Metals at the surface of last scatter

2011

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Standard big-bang nucleosynthesis (BBN) predicts only a trace abundance of lithium and no heavier elements, but some alternatives predict a nonzero primordial metallicity. Here we explore whether CMB measurements may set useful constraints to the primordial metallicity and/or whether the standard CMB calculations are robust, within the tolerance of forthcoming CMB maps, to the possibility of primordial metals. Metals would affect the recombination history (and thus CMB power spectra) in three ways: (1) Ly photons can be removed (and recombination thus accelerated) by photoionizing metals; (2) The Bowen resonance-fluorescence mechanism may degrade Ly photons and thus enhance the Ly escape probability and speed up recombination; (3) Metals could affect the low-redshift tail of the CMB visibility function by providing additional free electrons. The last two of these provide the strongest CMB signal. However, the effects are detectable in the Planck satellite only if the primordial metal abundance is at least a few hundredths of solar for (2) and a few tenths of solar for (3). We thus conclude that Planck will not be able to improve upon current constraints to primordial metallicity, at the level of a thousandth of solar, from the Lyman-forest and ultra-metal-poor halo stars, and that the CMB power-spectrum predictions for Planck suffer no uncertainty arising from the possibility that there may be primordial metals.

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Section: Effect Of Neutral Metals On the Lyman-decay Ratementioning

confidence: 95%

Metals at the surface of last scatter

2011

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“…Figure 6 shows how a higher helium fraction consistent with WMAP data (Y P = 0.5) is ruled out by ACT's determination of Silk damping at small scales. There is still some uncertainty in the exact details of recombination (e.g., Wong & Scott 2007;Chluba et al 2007;Switzer & Hirata 2008;Fendt et al 2009;Chluba & Sunyaev 2010). A recent refinement of the numerical code for recombination used for this analysis (Recfast 1.5, by Seager et al 1999, updated to match Rubiño-Martín et al 2010, gives a 2% change in the spectrum at = 2000.…”

Section: Primordial 4 He Abundancementioning

confidence: 99%

The Atacama Cosmology Telescope: Cosmological Parameters From the 2008 Power Spectrum

Dunkley

Hložek

Sievers

et al. 2011

ApJ

362

454

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We present cosmological parameters derived from the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz over 296 deg 2 with the Atacama Cosmology Telescope (ACT) during its 2008 season. ACT measures fluctuations at scales 500 < < 10,000. We fit a model for the lensed CMB, Sunyaev-Zel'dovich (SZ), and foreground contribution to the 148 GHz and 218 GHz power spectra, including thermal and kinetic SZ, Poisson power from radio and infrared point sources, and clustered power from infrared point sources. At = 3000, about half the power at 148 GHz comes from primary CMB after masking bright radio sources. The power from thermal and kinetic SZ is estimated to be B 3000 = 6.8 ± 2.9 μK 2 , where B ≡ ( + 1)C /2π . The IR Poisson power at 148 GHz is B 3000 = 7.8 ± 0.7 μK 2 (C = 5.5 ± 0.5 nK 2 ), and a clustered IR component is required with B 3000 = 4.6 ± 0.9 μK 2 , assuming an analytic model for its power spectrum shape. At 218 GHz only about 15% of the power, approximately 27 μK 2 , is CMB anisotropy at = 3000. The remaining 85% is attributed to IR sources (approximately 50% Poisson and 35% clustered), with spectral index α = 3.69 ± 0.14 for flux scaling as S(ν) ∝ ν α . We estimate primary cosmological parameters from the less contaminated 148 GHz spectrum, marginalizing over SZ and source power. The ΛCDM cosmological model is a good fit to the data (χ 2 /dof = 29/46), and ΛCDM parameters estimated from ACT+Wilkinson Microwave Anisotropy Probe (WMAP) are consistent with the seven-year WMAP limits, with scale invariant n s = 1 excluded at 99.7% confidence level (CL) (3σ ). A model with no CMB lensing is disfavored at 2.8σ . By measuring the third to seventh acoustic peaks, and probing the Silk damping regime, the ACT data improve limits on cosmological parameters that affect the small-scale CMB power. The ACT data combined with WMAP give a 6σ detection of primordial helium, with Y P = 0.313 ± 0.044, and a 4σ detection of relativistic species, assumed to be neutrinos, with N eff = 5.3 ± 1.3 (4.6 ± 0.8 with BAO+H 0 data). From the CMB alone the running of the spectral index is constrained to be dn s /d ln k = −0.034 ± 0.018, the limit on the tensor-to-scalar ratio is r < 0.25 (95% CL), and the possible contribution of Nambu cosmic strings to the power spectrum is constrained to string tension Gμ < 1.6 × 10 −7 (95% CL).

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“…In particular, C. Hirata and E. Switzer have rigorously studied these and several additional processes (Switzer & Hirata 2008aHirata & Switzer 2008). However, since the details of helium recombination history are not strongly propagating to the computation of the CMB power spectra, as a first step here we only include the two dominant corrections, which actually are due to processes that have no analog in the case of hydrogen recombination.…”

Section: Processes Included During Helium Recombinationmentioning

confidence: 99%

Rico: A New Approach for Fast and Accurate Representation of the Cosmological Recombination History

Fendt

Chluba

Rubiño-Martín

et al. 2009

ApJS

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We present Rico, a code designed to compute the ionization fraction of the universe during the epoch of hydrogen and helium recombination with an unprecedented combination of speed and accuracy. This is accomplished by training the machine learning code Pico on the calculations of a multilevel cosmological recombination code which self-consistently includes several physical processes that were neglected previously. After training, Rico is used to fit the free electron fraction as a function of the cosmological parameters. While, for example, at low redshifts (z 900), much of the net change in the ionization fraction can be captured by lowering the hydrogen fudge factor in Recfast by about 3%, Rico provides a means of effectively using the accurate ionization history of the full recombination code in the standard cosmological parameter estimation framework without the need to add new or refined fudge factors or functions to a simple recombination model. Within the new approach presented here, it is easy to update Rico whenever a more accurate full recombination code becomes available. Once trained, Rico computes the cosmological ionization history with negligible fitting error in ∼10 ms, a speedup of at least 10 6 over the full recombination code that was used here. Also Rico is able to reproduce the ionization history of the full code to a level well below 0.1%, thereby ensuring that the theoretical power spectra of cosmic microwave background (CMB) fluctuations can be computed to sufficient accuracy and speed for analysis from upcoming CMB experiments like Planck. Furthermore, it will enable cross-checking different recombination codes across cosmological parameter space, a comparison that will be very important in order to assure the accurate interpretation of future CMB data.

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Primordial helium recombination. I. Feedback, line transfer, and continuum opacity

Cited by 86 publications

References 82 publications

Metals at the surface of last scatter

Metals at the surface of last scatter

The Atacama Cosmology Telescope: Cosmological Parameters From the 2008 Power Spectrum

Rico: A New Approach for Fast and Accurate Representation of the Cosmological Recombination History

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