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1. Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) – XV. Constraining the cosmic reionization at 5.5 < z < 7

   https://doi.org/10.1093/mnras/stac2681  

   Lu, Ting-Yi ; Goto, Tomotsugu ; Hashimoto, Tetsuya ; Santos, Daryl Joe D. ; Wong, Yi Hang Valerie ; Kim, Seong Jin ; Hsiao, Tiger Y-Y ; Kilerci, Ece ; Ho, Simon C-C ; Nagao, Tohru ; et al ( September 2022 , Monthly Notices of the Royal Astronomical Society)

   Revealing the cosmic hydrogen reionization history is one of the main goals of the modern cosmology. z > 5 quasars (QSOs) have been used as back-lights to investigate the evolution of the intervening intergalactic medium (IGM) during the cosmic reionization since their first discovery. However, due to the small population of luminous QSOs (∼130 QSOs known to date), a tight constraint on the reionization history has not yet been placed. In this work, we aim to tighten the constraint using the 93 QSOs (5.5 < z < 7.1) recently discovered in the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQS) project. This is the largest QSO sample used to constrain the epoch of reionization. We measure the mean IGM Ly α transmission and the QSO near-zone size using the UV spectra of these QSOs. The mean IGM Ly α transmission rises above zero at z ≲ 6, indicating the end of the reionization. The near-zone sizes of the SHELLQs QSOs are consistent with sizes spanned by QSOs of lifetime tq ∼ 1–100 Myr in simulations. Due to the scatter created by the low signal-to-noise spectra and large Ly α redshift uncertainty, we cannot conclude whether the redshift evolution of the near-zone size is affected by the reionization effect.

    

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2. Chasing the Tail of Cosmic Reionization with Dark Gap Statistics in the Lyα Forest over 5 < z < 6

   https://doi.org/10.3847/1538-4357/ac26c2  

   Zhu, Yongda ; Becker, George D. ; Bosman, Sarah E. ; Keating, Laura C. ; Christenson, Holly M. ; Bañados, Eduardo ; Bian, Fuyan ; Davies, Frederick B. ; D’Odorico, Valentina ; Eilers, Anna-Christina ; et al ( December 2021 , The Astrophysical Journal)

   Abstract We present a new investigation of the intergalactic medium (IGM) near the end of reionization using “dark gaps” in the Ly α forest. Using spectra of 55 QSOs at z em > 5.5, including new data from the XQR-30 VLT Large Programme, we identify gaps in the Ly α forest where the transmission averaged over 1 comoving h −1 Mpc bins falls below 5%. Nine ultralong ( L > 80 h −1 Mpc) dark gaps are identified at z < 6. In addition, we quantify the fraction of QSO spectra exhibiting gaps longer than 30 h −1 Mpc, F 30 , as a function of redshift. We measure F 30 ≃ 0.9, 0.6, and 0.15 at z = 6.0, 5.8, and 5.6, respectively, with the last of these long dark gaps persisting down to z ≃5.3. Comparing our results with predictions from hydrodynamical simulations, we find that the data are consistent with models wherein reionization extends significantly below redshift six. Models wherein the IGM is essentially fully reionized that retain large-scale fluctuations in the ionizing UV background at z ≲6 are also potentially consistent with the data. Overall, our results suggest that signatures of reionization in the form of islands of neutral hydrogen and/or large-scale fluctuations in the ionizing background remain present in the IGM until at least z ≃ 5.3. 

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3. Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 < z < 6

   https://doi.org/10.3847/1538-4357/aceef4  

   Zhu, Yongda ; Becker, George D. ; Christenson, Holly M. ; D’Aloisio, Anson ; Bosman, Sarah E. I. ; Bakx, Tom ; D’Odorico, Valentina ; Bischetti, Manuela ; Cain, Christopher ; Davies, Frederick B. ; et al ( September 2023 , The Astrophysical Journal)

   The mean free path of ionizing photons,λ_mfp, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements ofλ_mfpfrom QSO spectra over the redshift range 5 <z< 6, including the first measurements atz≃ 5.3 and 5.6. Our sample includes data from the XQR-30 VLT large program, as well as new Keck/ESI observations of QSOs nearz∼ 5.5, for which we also acquire new [Cii] 158μm redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find${\lambda }_{\mathrm{mfp}}={9.33}_{-1.80}^{+2.06}$,${5.40}_{-1.40}^{+1.47}$,${3.31}_{-1.34}^{+2.74}$, and${0.81}_{-0.48}^{+0.73}$pMpc atz= 5.08, 5.31, 5.65, and 5.93, respectively. Our results demonstrate thatλ_mfpincreases steadily and rapidly with time over 5 <z< 6. Notably, we find thatλ_mfpdeviates significantly from predictions based on a fully ionized and relaxed IGM as late asz= 5.3. By comparing our results to model predictions and indirectλ_mfpconstraints based on IGM Lyαopacity, we find that the evolution ofλ_mfpis consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6.

    

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4. Long Dark Gaps in the Lyβ Forest at z < 6: Evidence of Ultra-late Reionization from XQR-30 Spectra

   https://doi.org/10.3847/1538-4357/ac6e60  

   Zhu, Yongda ; Becker, George D. ; Bosman, Sarah E. I. ; Keating, Laura C. ; D’Odorico, Valentina ; Davies, Rebecca L. ; Christenson, Holly M. ; Bañados, Eduardo ; Bian, Fuyan ; Bischetti, Manuela ; et al ( June 2022 , The Astrophysical Journal)

   We present a new investigation of the intergalactic medium near reionization using dark gaps in the Lyβforest. With its lower optical depth, Lyβoffers a potentially more sensitive probe to any remaining neutral gas compared to the commonly used Lyαline. We identify dark gaps in the Lyβforest using spectra of 42 QSOs atz_em> 5.5, including new data from the XQR-30 VLT Large Programme. Approximately 40% of these QSO spectra exhibit dark gaps longer than 10h⁻¹Mpc atz≃ 5.8. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Lyαforest are caused solely by ionizing ultraviolet background fluctuations and with models that include large neutral hydrogen patches atz< 6 due to a late end to reionization. Of particular interest is a very long (L= 28h⁻¹Mpc) and dark (τ_eff≳ 6) gap persisting down toz≃ 5.5 in the Lyβforest of thez= 5.85 QSO PSO J025−11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of 〈x_{H I}〉 ≳ 5% byz= 5.6. Finally, we infer constraints on 〈x_{H I}〉 over 5.5 ≲z≲ 6.0 based on the observed Lyβdark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find 〈x_{H I}〉 ≤ 0.05, 0.17, and 0.29 atz≃ 5.55, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later thanz= 6.

    

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5. Ultraluminous high-redshift quasars from SkyMapper – II. New quasars and the bright end of the luminosity function

   https://doi.org/10.1093/mnras/stac051  

   Onken, Christopher A. ; Wolf, Christian ; Bian, Fuyan ; Fan, Xiaohui ; Hon, Wei Jeat ; Raithel, David ; Tisserand, Patrick ; Lai, Samuel ( January 2022 , Monthly Notices of the Royal Astronomical Society)

   We search for ultraluminous Quasi-Stellar Objects (QSOs) at high redshift using photometry from the SkyMapper Southern Survey Data Release 3 (DR3), in combination with 2MASS, VHS DR6, VIKING DR5, AllWISE, and CatWISE2020, as well as parallaxes and proper motions from Gaia DR2 and eDR3. We report 142 newly discovered Southern QSOs at 3.8 < z < 5.5, of which 126 have M145 < −27 AB mag and are found in a search area of 14 486 deg2. This Southern sample, utilizing the Gaia astrometry to offset wider photometric colour criteria, achieves unprecedented completeness for an ultraluminous QSO search at high redshift. In combination with already known QSOs, we construct a sample that is >80 per cent complete for M145 < −27.33 AB mag at z = 4.7 and for M145 < −27.73 AB mag at z = 5.4. We derive the bright end of the QSO luminosity function at rest frame 145 nm for z = 4.7–5.4 and measure its slope to be β = −3.60 ± 0.37 and β = −3.38 ± 0.32 for two different estimates of the faint-end QSO density adopted from the literature. We also present the first z ∼ 5 QSO luminosity function at rest frame 300 nm.

    

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