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1. The Relationship between IGM Lyα Opacity and Galaxy Density near the End of Reionization

   https://doi.org/10.3847/1538-4357/acf450  

   Christenson, Holly M. ; Becker, George D. ; D’Aloisio, Anson ; Davies, Frederick B. ; Zhu, Yongda ; Boera, Elisa ; Nasir, Fahad ; Furlanetto, Steven R. ; Malkan, Matthew A. ( September 2023 , The Astrophysical Journal)

   Observed scatter in the Lyαopacity of quasar sightlines atz< 6 has motivated measurements of the correlation between Lyαopacity and galaxy density, as models that predict this scatter make strong and sometimes opposite predictions for how they should be related. Our previous work associated two highly opaque Lyαtroughs atz∼ 5.7 with a deficit of Lyαemitting galaxies (LAEs). In this work, we survey two of the most highly transmissive lines of sight at this redshift toward thez= 6.02 quasar SDSS J1306+0356 and thez= 6.17 quasar PSO J359-06. We find that both fields are underdense in LAEs within 10h⁻¹Mpc of the quasar sightline, somewhat less extensive than underdensities associated with Lyαtroughs. We combine our observations with three additional fields from the literature and find that while fields with extreme opacities are generally underdense, moderate opacities span a wider density range. The results at high opacities are consistent with models that invoke UV background fluctuations and/or late reionization to explain the observed scatter in intergalactic medium (IGM) Lyαopacities. There is tension at low opacities, however, as the models tend to associate lower IGM Lyαopacities with higher densities. Although the number of fields surveyed is still small, the low-opacity results may support a scenario in which the ionizing background in low-density regions increases more rapidly than some models suggest after becoming ionized. Elevated gas temperatures from recent reionization may also be making these regions more transparent.

    

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2. Hydrogen reionization ends by z = 5.3: Lyman-α optical depth measured by the XQR-30 sample

   https://doi.org/10.1093/mnras/stac1046  

   Bosman, Sarah E ; Davies, Frederick B ; Becker, George D ; Keating, Laura C ; Davies, Rebecca L ; Zhu, Yongda ; Eilers, Anna-Christina ; D’Odorico, Valentina ; Bian, Fuyan ; Bischetti, Manuela ; et al ( June 2022 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The presence of excess scatter in the Ly-α forest at z ∼ 5.5, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionization. However, low data quality and systematic uncertainties complicate the use of Ly-α transmission as a precision probe of reionization’s end stages. In this paper, we assemble a sample of 67 quasar sightlines at z > 5.5 with high signal-to-noise ratios of >10 per ≤15 km s−1 spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR > 20 per pixel) spectra of 30 quasars at z > 5.7. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-α systems. We present improved measurements of the mean Ly-α transmission over 4.9 < z < 6.1. Using all known systematics in a forward modelling analysis, we find excellent agreement between the observed Ly-α transmission distributions and the homogeneous-UVB simulations Sherwood and Nyx up to z ≤ 5.2 (<1σ), and mild tension (∼2.5σ) at z = 5.3. Homogeneous UVB models are ruled out by excess Ly-α transmission scatter at z ≥ 5.4 with high confidence (>3.5σ). Our results indicate that reionization-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least z = 5.3 (t = 1.1 Gyr after the big bang). This is further evidence for a late end to reionization. 

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3. Constraining reionization in progress at z  = 5.7 with Lyman-α emitters: voids, peaks, and cosmic variance

   https://doi.org/10.1093/mnras/staa3843  

   Gangolli, Nakul ; D’Aloisio, Anson ; Nasir, Fahad ; Zheng, Zheng ( January 2021 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT A number of independent observations suggest that the intergalactic medium was significantly neutral at z = 7 and that reionization was, perhaps, still in progress at z = 5.7. The narrowband survey, SILVERRUSH, has mapped over 2000 Lyman-α emitters (LAEs) at these redshifts ( G58). Previous analyses have assumed that reionization was over by z = 5.7, but this data may actually sample the final stages of reionization when the last neutral islands were relegated to the cosmic voids. Motivated by these developments, we re-examine LAE void and peak statistics and their ability to constrain reionization. We construct models of the LAE distribution in (1 Gpc h−1)3 volumes, spanning a range of neutral fractions at z = 5.7 and 6.6. Models with a higher neutral fraction show an enhanced probability of finding holes in the LAE distribution. When comparing models at fixed mean surface density, however, LAEs obscured by neutral gas in the voids must be compensated by visible LAEs elsewhere. Hence, in these models, the likelihood of finding an overdense peak is also enhanced in the latter half of reionization. Compared to the widely used angular two-point correlation function (2PCF), we find that the void probability function (VPF) provides a more sensitive test of models during the latter half of reionization. By comparison, at neutral fractions $\sim 50{{\ \rm per\ cent}}$, the VPF and a simple peak thresholding statistic are both similar to the 2PCF in constraining power. Lastly, we find that the cosmic variance and large-scale asymmetries observed in the SILVERRUSH fields are consistent with large-scale structure in a ΛCDM universe. 

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4. Insight from JWST /Near Infrared Camera into galaxy overdensities around bright Lyman-alpha emitters during reionization: implications for ionized bubbles at z ∼ 9

   https://doi.org/10.1093/mnras/stae516  

   Whitler, Lily ; Stark, Daniel P. ; Endsley, Ryan ; Chen, Zuyi ; Mason, Charlotte ; Topping, Michael W. ; Charlot, Stéphane ( February 2024 , Monthly Notices of the Royal Astronomical Society)

   Several studies have detected Lyman-alpha (Ly α) from bright ($M_{\small UV}\lesssim -21.5$) galaxies during the early stages of reionization despite the significantly neutral intergalactic medium. To explain these detections, it has been suggested that z > 7 Ly α emitters (LAEs) inhabit physical Mpc (pMpc)-scale ionized regions powered by overdensities of faint galaxies; however, systematic searches for these overdensities near LAEs have been challenging. Here, we use Cosmic Evolution Early Release Science JWST/Near Infrared Camera imaging to search for large-scale galaxy overdensities near two very ultraviolet (UV)-bright, z = 8.7 LAEs in the Extended Groth Strip (EGS) field. We colour select 27 z = 8.4–9.1 candidates, including the one LAE in the footprint (EGSY8p7). From spectral energy distribution models, we infer moderately faint UV luminosities ($-21.2\lesssim {M_{\small UV}}\lesssim -19.1$) and stellar masses of M* ≈ 107.5–8.8 M⊙. All are efficient ionizing agents ($\xi _{\text{ion}}^{*}\approx 10^{25.5-26.0}$ Hz erg−1) and are generally morphologically simple with only one compact (re ≲ 140 to ∼650 pc) star-forming component. 13 candidates lie within 5 arcmin of EGSY8p7, leading to a factor-of-four galaxy overdensity at ≲5 arcmin (∼1.4 projected pMpc at z ∼ 8.7) separations from EGSY8p7. Separations of 10–15 arcmin (∼2.7–4.1 projected pMpc) are consistent with an average field. The spatial distribution of our sample may qualitatively suggest an R ≥ 2 pMpc ionized bubble encompassing both LAEs in EGS, which is theoretically unexpected but may be possible for a galaxy population four times more numerous than the average to create with moderate escape fractions (fesc ≳ 0.15) over long times (≳ 200 Myr). Upcoming spectroscopic follow-up will characterize the size of any ionized bubble that may exist and the properties of the galaxies powering such a bubble.

    

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5. A Massive Protocluster Anchored by a Luminous Quasar at z = 6.63

   https://doi.org/10.3847/2041-8213/ad20ef  

   Wang, Feige ; Yang, Jinyi ; Hennawi, Joseph F. ; Fan, Xiaohui ; Yue, Minghao ; Bañados, Eduardo ; Bechtel, Shane ; Bian, Fuyan ; Bosman, Sarah ; Champagne, Jaclyn B. ; et al ( February 2024 , The Astrophysical Journal Letters)

   Protoclusters, the progenitors of galaxy clusters, trace large scale structures in the early Universe and are important to our understanding of structure formation and galaxy evolution. To date, only a handful of protoclusters have been identified in the Epoch of Reionization. As one of the rarest populations in the early Universe, distant quasars that host active supermassive black holes are thought to reside in the most massive dark matter halos at that cosmic epoch and could thus potentially pinpoint some of the earliest protoclusters. In this Letter, we report the discovery of a massive protocluster around a luminous quasar atz= 6.63. This protocluster is anchored by the quasar and includes three [Cii] emitters atz∼ 6.63, 12 spectroscopically confirmed Lyαemitters (LAEs) at 6.54 <z≤ 6.64, and a large number of narrow-band-imaging selected LAE candidates at the same redshift. This structure has an overall overdensity of$\delta ={3.3}_{-0.9}^{+1.1}$within ∼35 × 74 cMpc²on the sky and an extreme overdensity ofδ> 30 in its central region (i.e.,R≲ 2 cMpc). We estimate that this protocluster will collapse into a galaxy cluster with a mass of${6.9}_{-1.4}^{+1.2}\times {10}^{15}{M}_{\odot }$at the current epoch, more massive than the most massive clusters known in the local Universe such as Coma. In the quasar vicinity, we discover a double-peaked LAE, which implies that the quasar has a UV lifetime greater than 0.8 Myrs and has already ionized its surrounding intergalactic medium.

    

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