Bosman, SEI;
Ďurovčíková, D;
Davies, FB;
Eilers, AC;
(2021)
A comparison of quasar emission reconstruction techniques for z ≥ 5.0 Lyman α and Lyman β transmission.
Monthly Notices of the Royal Astronomical Society
, 503
(2)
pp. 2077-2096.
10.1093/mnras/stab572.
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Abstract
Reconstruction techniques for intrinsic quasar continua are crucial for the precision study of Lyman-$\alpha$ (Ly-$\alpha$) and Lyman-$\beta$ (Ly-$\beta$) transmission at $z>5.0$, where the $\lambda<1215 A$ emission of quasars is nearly completely absorbed. While the number and quality of spectroscopic observations has become theoretically sufficient to quantify Ly-$\alpha$ transmission at $5.0<z<6.0$ to better than $1\%$, the biases and uncertainties arising from predicting the unabsorbed continuum are not known to the same level. In this paper, we systematically evaluate eight reconstruction techniques on a unified testing sample of $2.7<z<3.5$ quasars drawn from eBOSS. The methods include power-law extrapolation, stacking of neighbours, and six variants of Principal Component Analysis (PCA) using direct projection, fitting of components, or neural networks to perform weight mapping. We find that power-law reconstructions and the PCA with fewest components and smallest training sample display the largest biases in the Ly-$\alpha$ forest ($-9.58\%/+8.22\%$ respectively). Power-law extrapolations have larger scatters than previously assumed of $+13.1\%/-13.2\%$ over Ly-$\alpha$ and $+19.9\%/-20.1\%$ over Ly-$\beta$. We present two new PCAs which achieve the best current accuracies of $9\%$ for Ly-$\alpha$ and $17\%$ for Ly-$\beta$. We apply the eight techniques after accounting for wavelength-dependent biases and scatter to a sample $19$ quasars at $z>5.7$ with IR X-Shooter spectroscopy, obtaining well-characterised measurements for the mean flux transmission at $4.7<z<6.3$. Our results demonstrate the importance of testing and, when relevant, training, continuum reconstruction techniques in a systematic way.
| Type: | Article |
|---|---|
| Title: | A comparison of quasar emission reconstruction techniques for z ≥ 5.0 Lyman α and Lyman β transmission |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/stab572 |
| Publisher version: | http://dx.doi.org/10.1093/mnras/stab572 |
| Language: | English |
| Additional information: | This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | methods: statistical, quasars: emission lines, dark ages, reionization, first stars |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10136058 |
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