Effective conductance method for the primordial recombination spectrum
Nov, 201214 pages
Published in:
- Phys.Rev.D 87 (2013) 2, 023526
- Published: Jan 25, 2013
e-Print:
- 1211.4031 [astro-ph.CO]
View in:
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Abstract: (APS)
As atoms formed for the first time during primordial recombination, they emitted bound-bound and free-bound radiation leading to spectral distortions to the cosmic microwave background. These distortions might become observable in the future with high-sensitivity spectrometers, and provide a new window into physical conditions in the early universe. The standard multilevel atom method habitually used to compute the recombination spectrum is computationally expensive, impeding a detailed quantitative exploration of the information contained in spectral distortions thus far. In this work it is shown that the emissivity in optically thin allowed transitions can be factored into a computationally expensive but cosmology-independent part and a computationally cheap, cosmology-dependent part. The slow part of the computation consists in pre-computing temperature-dependent effective “conductances,” linearly relating line or continuum intensity to departures from Saha equilibrium of the lowest-order excited states (2s and 2p), that can be seen as “voltages.” The computation of these departures from equilibrium as a function of redshift is itself very fast, thanks to the effective multilevel atom method introduced in an earlier work. With this factorization, the recurring cost of a single computation of the recombination spectrum is only a fraction of a second on a standard laptop, more than four orders of magnitude shorter than standard computations. The spectrum from helium recombination can be efficiently computed in an identical way, and a fast code computing the full primordial recombination spectrum with this method will be made publicly available soon.Note:
- 14 pages, 5 figures. Submitted to Phys. Rev. D. Comments are welcome
- 98.70.Vc
- 32.80.Rm
- 98.80.-k
- 78.60.-b
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Figures(7)
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