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ABSTRACT We introduce a new approach for analysing the intergalactic medium (IGM) damping wings imprinted on the proximity zones of quasars in the epoch of reionization (EoR). Whereas past work has typically forgone the additional constraining power afforded by the blue side continuum ($$\lambda \lesssim 1280\,$$ Å) and/or opted not to model the large correlated IGM transmission fluctuations in the proximity zone ($$\lambda \lesssim 1216\,$$ Å), we construct a generative probabilistic model for the entire spectrum accounting for all sources of error – the stochasticity induced by patchy reionization, the impact of the quasar’s ionizing radiation on the IGM, the unknown intrinsic spectrum of the quasar, and spectral noise. This principled Bayesian method allows us to marginalize out nuisance parameters associated with the quasar’s radiation and its unknown intrinsic spectrum to precisely measure the IGM neutral fraction, $$\langle x_{\rm H\,\small{I}}\rangle$$. A key element of our analysis is the use of dimensionality reduction (DR) to describe the intrinsic quasar spectrum via a small number of nuisance parameters. Using a large sample of 15 559 SDSS/BOSS quasars at $$z \gtrsim 2.15$$ we trained and quantified the performance of six distinct DR methods, and find that a six parameter principal component analysis model (five coefficients plus a normalization) performs best, with complex machine-learning approaches providing no advantage. By conducting statistical inference on 100 realistic mock EoR quasar spectra, we demonstrate the reliability of the credibility contours that we obtain on $$\langle x_{\rm H\,{\small{I}}}\rangle$$ and the quasar lifetime, $$t_{\rm Q}$$. The new method introduced here will transform IGM damping wings into a precision probe of reionization, on the same solid methodological and statistical footing as other precision cosmological measurements.
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Measuring the photoionization rate, neutral fraction, and mean free path of H i ionizing photons at 4.9 ≤ z ≤ 6.0 from a large sample of XShooter and ESI spectra
ABSTRACT We measure the mean free path ($$\lambda _{\rm mfp,H\, \small {I}}$$), photoionization rate ($$\langle \Gamma _{\rm H\, \small {I}} \rangle$$), and neutral fraction ($$\langle f_{\rm H\, \small {I}} \rangle$$) of hydrogen in 12 redshift bins at 4.85 < z < 6.05 from a large sample of moderate resolution XShooter and ESI QSO absorption spectra. The fluctuations in ionizing radiation field are modelled by post-processing simulations from the Sherwood suite using our new code ‘EXtended reionization based on the Code for Ionization and Temperature Evolution’ (ex-cite). ex-cite uses efficient Octree summation for computing intergalactic medium attenuation and can generate large number of high resolution $$\Gamma _{\rm H\, \small {I}}$$ fluctuation models. Our simulation with ex-cite shows remarkable agreement with simulations performed with the radiative transfer code Aton and can recover the simulated parameters within 1σ uncertainty. We measure the three parameters by forward-modelling the Lyα forest and comparing the effective optical depth ($$\tau _{\rm eff, H\, \small {I}}$$) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modelling parameters, observational systematics, and cosmic variance. Our best-fitting parameters show significant evolution with redshift such that $$\lambda _{\rm mfp,H\, \small {I}}$$ and $$\langle f_{\rm H\, \small {I}} \rangle$$ decreases and increases by a factor ∼6 and ∼104, respectively from z ∼ 5 to z ∼ 6. By comparing our $$\lambda _{\rm mfp,H\, \small {I}}$$, $$\langle \Gamma _{\rm H\, \small {I}} \rangle$$ and $$\langle f_{\rm H\, \small {I}} \rangle$$ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best-fitting parameter evolution is consistent with a model in which reionization completes by z ∼ 5.2. Our best-fitting model that matches the $$\tau _{\rm eff, H\, \small {I}}$$ distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters.
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- Award ID(s):
- 1751404
- PAR ID:
- 10462433
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 525
- Issue:
- 3
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 4093-4120
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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