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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. 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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3. 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)
4. Probing Cosmic Reionization and Molecular Gas Growth with TIME

   https://doi.org/10.3847/1538-4357/abfe62  

   Sun, G.; Chang, T.-C.; Uzgil, B. D.; Bock, J. J.; Bradford, C. M.; Butler, V.; Caze-Cortes, T.; Cheng, Y.-T.; Cooray, A.; Crites, A. T.; et al (July 2021, The Astrophysical Journal)
5. Exploring the epoch of hydrogen reionization using FRBs

   https://doi.org/10.1093/mnras/stab309  

   Beniamini, Paz; Kumar, Pawan; Ma, Xiangcheng; Quataert, Eliot (March 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We describe three different methods for exploring the hydrogen reionization epoch using fast radio bursts (FRBs) and provide arguments for the existence of FRBs at high redshift (z). The simplest way, observationally, is to determine the maximum dispersion measure (DMmax) of FRBs for an ensemble that includes bursts during the reionization. The DMmax provides information regarding reionization much like the optical depth of the cosmic microwave background to Thomson scattering does, and it has the potential to be more accurate than constraints from Planck, if DMmax can be measured to a precision better than 500 pccm−3. Another method is to measure redshifts of about 40 FRBs between z of 6 and 10 with $${\sim}10{{\ \rm per\ cent}}$$ accuracy to obtain the average electron density in four different z-bins with $${\sim}4{{\ \rm per\ cent}}$$ accuracy. These two methods do not require knowledge of the FRB luminosity function and its possible redshift evolution. Finally, we show that the reionization history is reflected in the number of FRBs per unit DM, given a fluence limited survey of FRBs that includes bursts during the reionization epoch; we show using FIRE simulations that the contribution to DM from the FRB host galaxy and circumgalactic medium during the reionization era is a small fraction of the observed DM. This third method requires no redshift information but does require knowledge of the FRB luminosity function. 

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