Atomic, Molecular, and Optical Physics in the Early Universe: From Recombination to Reionization

Glover, Simon C. O.; Chluba, Jens; Furlanetto, Steve R.; Pritchard, Jonathan R.; Savin, D. W.

doi:10.1016/b978-0-12-800129-5.00003-1

Cited by 19 publications

(9 citation statements)

References 286 publications

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“…Another important transition occurred earlier at even higher redshifts, when during the epoch of recombination the primordial plasma recombined and the universe became neutral, with atomic hydrogen, helium, and a small fraction of light elements. While the physics of the epoch of recombination is well understood from the theoretical point of view (Ali-Haïmoud & Hirata 2011;Chluba & Thomas 2011;Glover et al 2014) and constrained by observations of the cosmic microwave background (CMB) (Calabrese et al 2013;Farhang et al 2013;Planck Collaboration et al 2016a), the EoR is relatively poorly understood. Among other aspects, the thermal evolution of baryons and nature of the first sources, the exact redshift and duration of reionization, and the dominant mechanisms that affect reionization are poorly constrained (Planck Collaboration et al 2016b).…”

Section: Introductionmentioning

confidence: 99%

Modeling the Radio Foreground for Detection of CMB Spectral Distortions from the Cosmic Dawn and the Epoch of Reionization

Rao

Subrahmanyan

Shankar

et al. 2017

ApJ

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Cosmic baryon evolution during the Cosmic Dawn and Reionization results in redshifted 21-cm spectral distortions in the cosmic microwave background (CMB). These encode information about the nature and timing of first sources over redshifts 30-6 and appear at meter wavelengths as a tiny CMB distortion along with the Galactic and extragalactic radio sky, which is orders of magnitude brighter. Therefore, detection requires precise methods to model foregrounds. We present a method of foreground fitting using maximally smooth (MS) functions. We demonstrate the usefulness of MS functions over traditionally used polynomials to separate foregrounds from the Epoch of Reionization (EoR) signal. We also examine the level of spectral complexity in plausible foregrounds using GMOSS, a physically motivated model of the radio sky, and find that they are indeed smooth and can be modeled by MS functions to levels sufficient to discern the vanilla model of the EoR signal. We show that MS functions are loss resistant and robustly preserve EoR signal strength and turning points in the residuals. Finally, we demonstrate that in using a well-calibrated spectral radiometer and modeling foregrounds with MS functions, the global EoR signal can be detected with a Bayesian approach with 90% confidence in 10 minutes' integration.

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Section: Introductionmentioning

confidence: 99%

Modeling the Radio Foreground for Detection of CMB Spectral Distortions from the Cosmic Dawn and the Epoch of Reionization

Rao

Subrahmanyan

Shankar

et al. 2017

ApJ

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“…As pointed out previously (e.g., Rubiño-Martín et al 2008;Chluba & Sunyaev 2010;Glover et al 2014), for the CRR one of the biggest uncertainty in the neutral helium model is due to the lack of data for the photoionization cross sections. For levels with n ≤ 10 and l ≤ 3, we use a combination of the sparse TopBase data (Cunto et al 1993) and pre-calculated recombination rates from Smits (1996).…”

Section: Photoionization Cross Sectionmentioning

confidence: 85%

cosmospec: fast and detailed computation of the cosmological recombination radiation from hydrogen and helium

Chluba

Ali-Haı̈moud

2016

Mon. Not. R. Astron. Soc.

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We present the first fast and detailed computation of the cosmological recombination radiation released during the hydrogen (redshift z 1300) and helium (z 2500 and z 6000) recombination epochs, introducing the code CosmoSpec. Our computations include important radiative transfer effects, 500-shell bound-bound and free-bound emission for all three species, the effects of electron scattering and free-free absorption as well as interspecies (He ii → He i → H i) photon feedback. The latter effect modifies the shape and amplitude of the recombination radiation and CosmoSpec improves significantly over previous treatments of it. Utilizing effective multilevel atom and conductance approaches, one calculation takes only 15 seconds on a standard laptop as opposed to days for previous computations. This is an important step towards detailed forecasts and feasibility studies considering the detection of the cosmological recombination lines and what one may hope to learn from the 6.1 photons emitted per hydrogen atom in the three recombination eras. We briefly illustrate some of the parameter dependencies and discuss remaining uncertainties in particular related to collisional processes and the neutral helium atom model.

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“…Finally, it is important to recall here that SSC rates have been used recently in CRR calculations (Chluba & Ali-Haïmoud 2016;Glover et al 2014), where a high precision of ∼ 0.1% is required (see Section 1). In Fig.…”

Section: Discussionmentioning

confidence: 99%

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

Guzmán

Badnell

Chatzikos

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abundances and recombination. There are now several competing theories for the treatment of this process, and it is not possible to test these experimentally. We show that the H I two-photon continuum produced by astrophysical nebulae is strongly affected by l-changing collisions. We perform an analysis of the different underlying atomic processes and simulate the recombination and two-photon spectrum of a nebula containing H and He. We provide an extended set of effective recombination coefficients and updated l-changing 2s − 2p transition rates using several competing theories. In principle, accurate astronomical observations could determine which theory is correct.Key words: cosmology: cosmic background radiation -cosmology: observations -atomic data -atomic processes -H ii regions -planetary nebulae: general MOTIVATIONOptical recombination lines (ORL) are produced from recombination of ions followed by cascades from highly excited recombined levels. Theoretical emissivities of these lines should be known with high accuracy, and observations of such lines in nebulae provide valuable and accurate information on their composition, temperature and density. This is summarized in the textbook of Osterbrock & Ferland (2006), while Schirmer (2016) applies this theory to spectral simulations.Although many processes contribute to the formation of these lines, recently attention has been brought to l-changing collisions. These act to redistribute the populations within an n-shell and so change the subsequent cascade to lower levels. Intra n-shell l-levels are energy degenerate for hydrogenic systems, so the orbiting electron changes its angular momentum with no energy change. This is caused by a long range Stark interaction with the electric field of the projectile. Due to this peculiarity, slow high-mass projectiles are favored over electrons.There are now several competing theories for how l-changing collisions occur, as summarized in our previous work (Guzmán et al. 2016(Guzmán et al. , 2017, hereafter P1 and P2, and in the next section. These have an important effect on recombination line intensities, as shown in P1 and P2. In addition, l-mixing collisions in relatively low n-shells play an important role in producing cosmological recombination radiation (CRR; Chluba et al. 2010). In fact, Lyα and two-photon emissivities are the two bottlenecks at different redshifts: Lyα at z > 1300, and two-photon at lower redshift during the recombination epoch. Chluba & Sunyaev (2006) show that an accurate treatment of l-mixing collisions, and the 2s and 2p populations is needed to predict the CMB to a precision of ∼ 0.1%. These processes have a similar effect on helium recombination lines, which introduces uncertainties in measurements of the primordial helium abundance (Porter et al. 2009).It is not possible to experimentally determine which of the l-changing theories is correct. Measurements of l-changing rates have been d...

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Atomic, Molecular, and Optical Physics in the Early Universe: From Recombination to Reionization

Cited by 19 publications

References 286 publications

Modeling the Radio Foreground for Detection of CMB Spectral Distortions from the Cosmic Dawn and the Epoch of Reionization

Modeling the Radio Foreground for Detection of CMB Spectral Distortions from the Cosmic Dawn and the Epoch of Reionization

cosmospec: fast and detailed computation of the cosmological recombination radiation from hydrogen and helium

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

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