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Reconstruction techniques for intrinsic quasar continua are crucial for the precision study of Lyman α (Ly α) and Lyman β (Ly β) transmission at z > 5.5, where the λ < 1215 Å emission of quasars is nearly completely absorbed. While the number and quality of spectroscopic observations have become theoretically sufficient to quantify Ly α transmission at 5.0 < z < 6.0 to better than $1{{\ \rm per\ cent}}$, 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 the Extended Baryon Oscillation Spectroscopic Survey. 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 α forest (${-}9.58{{\ \rm per\ cent}}/{+}8.22{{\ \rm per\ cent}}$, respectively). Power-law extrapolations have larger scatters than previously assumed of ${+}13.1{{\ \rm per\ cent}}/{-}13.2{{\ \rm per\ cent}}$ over Ly α and ${+}19.9{{\ \rm per\ cent}}/{-}20.1{{\ \rm per\ cent}}$ over Ly β. We present two new PCAs that achieve the best current accuracies of $9{{\ \rm per\ cent}}$ for Ly α and $17{{\ \rm per\ cent}}$ for Ly β. We apply the eight techniques after accounting for wavelength-dependent biases and scatter to a sample of 19 quasars at z > 5.7 with IR X-Shooter spectroscopy, obtaining well-characterized 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.

Conventional laser cooling techniques have proved inefficient on mechani-cal oscillators heavier than a few nanograms. Here, we present a new approach to realize motional ground state cooling of such oscillators, paving the way to currently inaccessible experiments such as tests of gravity’s effect on massive quantum systems.

Identifying low-redshift galaxies that emit Lyman Continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly "analogues" of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at $z\sim3$ and $z\sim0$. We find that the simulated galaxies with high LyC escape fractions ($f_{\rm esc}$) often exhibit high O32 and populate the same regions of the R23-O32 plane as $z\sim3$ LyC leakers. However, we show that viewing angle, metallicity, and ionisation parameter can all impact where a galaxy resides on the O32-$f_{\rm esc}$ plane. Based on emission line diagnostics and how they correlate with $f_{\rm esc}$, lower-metallicity LyC leakers at $z\sim3$ appear to be good analogues of reionization-era galaxies. In contrast, local [SII]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the SII-BPT diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using IR and nebular emission lines. We show that our model using only [CII]$_{\rm 158\mu m}$ and [OIII]$_{\rm 88\mu m}$ can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS1149_JD1 at $z=9.1$ is the most likely galaxy to be actively contributing to the reionization of the Universe., Comment: 18 pages, 11 figures, Accepted to MNRAS

Observations of the early Universe suggest that reionization was complete by z ∼ 6, however, the exact history of this process is still unknown. One method for measuring the evolution of the neutral fraction throughout this epoch is via observing the Lyα damping wings of high-redshift quasars. In order to constrain the neutral fraction from quasar observations, one needs an accurate model of the quasar spectrum around Lyα, after the spectrum has been processed by its host galaxy but before it is altered by absorption and damping in the intervening intergalactic medium (IGM). In this paper, we present a novel machine learning approach, using artificial neural networks, to reconstruct quasar continua around Lyα. Our Quasar Spectra from Artificial Neural Network based predictive Regression Algorithm(QSANNdRA) improves the error in this reconstruction compared to the state-of-the-art principal component analysis (PCA) based model in the literature by 14.2 per cent on average, and provides an improvement of 6.1 per cent on average when compared to an extension thereof. In comparison with the extended PCA model, QSANNdRA further achieves an improvement of 22.1 per cent and 16.8 per cent when evaluated on low-redshift quasars most similar to the two high-redshift quasars under consideration, ULAS J1120+0641 at z = 7.0851 and ULAS J1342+0928 at z = 7.5413, respectively. Using our more accurate reconstructions of these two z > 7 quasars, we estimate the neutral fraction of the IGM using a homogeneous reionization model and find $\bar{x}_\mathrm{H\, \small{I}} = 0.25^{+0.05}_{-0.05}$ at z = 7.0851 and $\bar{x}_\mathrm{H\, \small{I}} = 0.60^{+0.11}_{-0.11}$ at z = 7.5413. Our results are consistent with the literature and favour a rapid end to reionization.