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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 Lya 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 Lya, 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 novelmachine 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 xHI = 0.25+0.05-0.05 at z = 7.0851 and xHI = 0.60+0.11-0.11 at z = 7.5413. Our results are consistent with the literature and favour a rapid end to reionization.

The detection of starlight from the host galaxies of quasars during the reionization epoch (z > 6) has been elusive, even with deep Hubble Space Telescope observations 1,2 . The current highest redshift quasar host detected 3 , at z = 4.5, required the magnifying effect of a foreground lensing galaxy. Low-luminosity quasars 4-6 from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) 7 mitigate the challenge of detecting their underlying, previously undetected host galaxies. Here we report rest-frame optical images and spectroscopy of two HSC-SSP quasars at z > 6 with the JWST. Using near-infrared camera imaging at 3.6 and 1.5 μm and subtracting the light from the unresolved quasars, we find that the host galaxies are massive (stellar masses of 13 × and 3.4 × 10 10  M ☉ , respectively), compact and disc-like. Near-infrared spectroscopy at medium resolution shows stellar absorption lines in the more massive quasar, confirming the detection of the host. Velocity-broadened gas in the vicinity of these quasars enables measurements of their black hole masses (1.4 × 10 9 and 2.0 × 10 8  M ☉ , respectively). Their location in the black hole mass-stellar mass plane is consistent with the distribution at low redshift, suggesting that the relation between black holes and their host galaxies was already in place less than a billion years after the Big Bang., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Bright quasars, powered by accretion onto billion-solar-mass black holes, already existed at the epoch of reionization, when the Universe was 0.5-1 billion years old 1 . How these black holes formed in such a short time is the subject of debate, particularly as they lie above the correlation between black-hole mass and galaxy dynamical mass 2,3 in the local Universe. What slowed down black-hole growth, leading towards the symbiotic growth observed in the local Universe, and when this process started, has hitherto not been known, although black-hole feedback is a likely driver 4 . Here we report optical and near-infrared observations of a sample of quasars at redshifts 5.8 ≲ z ≲ 6.6. About half of the quasar spectra reveal broad, blueshifted absorption line troughs, tracing black-hole-driven winds with extreme outflow velocities, up to 17% of the speed of light. The fraction of quasars with such outflow winds at z ≳ 5.8 is ≈2.4 times higher than at z ≈ 2-4. We infer that outflows at z ≳ 5.8 inject large amounts of energy into the interstellar medium and suppress nuclear gas accretion, slowing down black-hole growth. The outflow phase may then mark the beginning of substantial black-hole feedback. The red optical colours of outflow quasars at z ≳ 5.8 indeed suggest that these systems are dusty and may be caught during an initial quenching phase of obscured accretion 5 ., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Observations of the redshift z = 7.085 quasar J1120+0641 are used to search for variations of the fine structure constant, α, over the redshift range 5.5 to 7.1. Observations at z = 7.1 probe the physics of the universe at only 0.8 billion years old. These are the most distant direct measurements of α to date and the first measurements using a near-IR spectrograph. A new AI analysis method is employed. Four measurements from the x-shooter spectrograph on the Very Large Telescope (VLT) constrain changes in a relative to the terrestrial value (α 0 ). The weighted mean electromagnetic force in this location in the universe deviates from the terrestrial value by Δα/α = (α z - α 0 )/α 0 = (-2.18 ± 7.27) × 10 -5 , consistent with no temporal change. Combining these measurements with existing data, we find a spatial variation is preferred over a no-variation model at the 3.9σ level., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)