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1. The contribution of globular clusters to cosmic reionization

   https://doi.org/10.1093/mnras/stab1132  

   Ma, Xiangcheng; Quataert, Eliot; Wetzel, Andrew; Faucher-Giguère, Claude-André; Boylan-Kolchin, Michael (May 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We study the escape fraction of ionizing photons (fesc) in two cosmological zoom-in simulations of galaxies in the reionization era with halo mass Mhalo ∼ 1010 and $$10^{11}\, \mathrm{ M}_{\odot }$$ (stellar mass M* ∼ 107 and $$10^9\, \mathrm{ M}_{\odot }$$) at z = 5 from the Feedback in Realistic Environments project. These simulations explicitly resolve the formation of proto-globular clusters (GCs) self-consistently, where 17–39 per cent of stars form in bound clusters during starbursts. Using post-processing Monte Carlo radiative transfer calculations of ionizing radiation, we compute fesc from cluster stars and non-cluster stars formed during a starburst over ∼100 Myr in each galaxy. We find that the averaged fesc over the lifetime of a star particle follows a similar distribution for cluster stars and non-cluster stars. Clusters tend to have low fesc in the first few Myr, presumably because they form preferentially in more extreme environments with high optical depths; the fesc increases later as feedback starts to destroy the natal cloud. On the other hand, some non-cluster stars formed between cluster complexes or in the compressed shells at the front of a superbubble can also have high fesc. We find that cluster stars on average have comparable fesc to non-cluster stars. This result is robust across several star formation models in our simulations. Our results suggest that the fraction of ionizing photons from proto-GCs to cosmic reionization is comparable to the cluster formation efficiencies in high-redshift galaxies and thus proto-GCs likely contribute an appreciable fraction of photons but are not the dominant sources for reionization. 

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2. Reconstructing patchy helium reionization using the cosmic microwave background and large-scale structure

   https://doi.org/10.1088/1475-7516/2024/10/034  

   Çalışkan, Mesut; Anil_Kumar, Neha; Hotinli, Selim C; Kamionkowski, Marc (October 2024, Journal of Cosmology and Astroparticle Physics)

   Abstract The intergalactic helium became fully ionized by the end of cosmic noon (z∼ 2).Similarly to the reionization of hydrogen, helium reionization is expected to be patchy, driven by luminous quasars that ionize the intergalactic gas in their surrounding environment.Probing the morphology of ionized electrons during this epoch can provide crucial information about early structure formation, including the clustering and luminosities of quasars, the accretion rates, variability, and lifetimes of active galactic nuclei, as well as the growth and evolution of supermassive black holes.In this study, we present how measurements of the cosmic microwave background (CMB) can be used to reconstruct the optical-depth fluctuations resulting from patchy helium reionization.As helium reionization occurred at lower redshifts, upcoming probes of large-scale structure surveys will present a significant opportunity to enhance the prospects of probing this epoch by their combined analysis with the CMB.Using a joint information-matrix analysis of hydrogen and helium reionization, we show that near-future galaxy and CMB surveys will have enough statistical power to detect optical-depth fluctuations due to doubly-ionized helium, providing a way of measuring the redshift and duration of helium reionization to high significance.We also show that modeling uncertainties in helium reionization can impact the measurement precision of parameters characterizing hydrogen reionization. 

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3. The Cosmic Microwave Background Optical Depth Constrains the Duration of Reionization

   https://doi.org/10.3847/2041-8213/ade141  

   Cain, Christopher; Van_Engelen, Alexander; Croker, Kevin S; Kramer, Darby; D’Aloisio, Anson; Lopez, Garett (July 2025, The Astrophysical Journal Letters)

   Abstract Recently, it was pointed out that invoking a large value of the cosmic microwave background (CMB) optical depth,τ_CMB = 0.09, could help resolve tensions between Dark Energy Survey Instrument DR2 baryon acoustic oscillation data and the CMB. This is larger than the value ofτ_CMB = 0.058 measured from the Planck low-ℓpolarization data. Traditionally,τ_CMBis thought of as a constraint on reionization’s midpoint. However, recent observations and modeling of the Lyαforest of high-zquasars at 5 < z < 6 have tightly constrained the timing of the last 10%–20% of reionization, adding nuance to this interpretation. Here, we point out that fixing reionization’s endpoint, in accordance with the latest Lyαforest constraints, rendersτ_CMBa sensitive probe of the duration of reionization, as well as its midpoint. We compare low and high values ofτ_CMBto upper limits on the patchy kinematic Sunyaev–Zel'dovich (pkSZ) effect, another CMB observable that constrains reionization’s duration, and find that a value ofτ_CMB = 0.09 is in ≈2σtension with existing limits on the pkSZ from the South Pole Telescope (SPT). The strength of this tension is sensitive to the choices involved in modeling the other CMB foregrounds in the SPT measurement, and in the modeling of the pkSZ signal itself. 

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4. Reionization with Simba: How Much Does Astrophysics Matter in Modeling Cosmic Reionization?

   https://doi.org/10.3847/1538-4357/ac69e2  

   Hassan, Sultan; Davé, Romeel; McQuinn, Matthew; Somerville, Rachel S.; Keating, Laura C.; Anglés-Alcázar, Daniel; Villaescusa-Navarro, Francisco; Spergel, David N. (May 2022, The Astrophysical Journal)

   Abstract Traditional large-scale models of reionization usually employ simple deterministic relations between halo mass and luminosity to predict how reionization proceeds. We here examine the impact on modeling reionization of using more detailed models for the ionizing sources as identified within the 100 h −1 Mpc cosmological hydrodynamic simulation S imba , coupled with postprocessed radiative transfer. Comparing with simple (one-to-one) models, the main difference with using S imba sources is the scatter in the relation between dark matter halos and star formation, and hence ionizing emissivity. We find that, at the power spectrum level, the ionization morphology remains mostly unchanged, regardless of the variability in the number of sources or escape fraction. In particular, the power spectrum shape remains unaffected and its amplitude changes slightly by less than 5%–10%, throughout reionization, depending on the scale and neutral fraction. Our results show that simplified models of ionizing sources remain viable to efficiently model the structure of reionization on cosmological scales, although the precise progress of reionization requires accounting for the scatter induced by astrophysical effects. 

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5. Definitive upper bound on the negligible contribution of quasars to cosmic reionization

   https://doi.org/10.1038/s41550-022-01708-w  

   Jiang, Linhua; Ning, Yuanhang; Fan, Xiaohui; Ho, Luis C.; Luo, Bin; Wang, Feige; Wu, Jin; Wu, Xue-Bing; Yang, Jinyi; Zheng, Zhen-Ya (July 2022, Nature Astronomy)