IslandFAST: A Semi-numerical Tool for Simulating the Late Epoch of Reionization

Xu, Yuelong; Yue, Bin; Chen, Xuelei

doi:10.3847/1538-4357/aa7b71

Cited by 18 publications

(23 citation statements)

References 63 publications

(73 reference statements)

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“…The late neutral islands are instead dominated by the larger structures. The size distribution of neutral islands evolves slowly, but, in contrast to what was found by Xu et al (2017), does evolve to smaller sizes as reionization progresses.…”

Section: Summary and Discussioncontrasting

confidence: 64%

Neutral island statistics during reionization from 21-cm tomography

Giri

Mellema

Aldheimer

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present the prospects of extracting information about the Epoch of Reionization by identifying the remaining neutral regions, referred to as islands, in tomographic observations of the redshifted 21-cm signal. Using simulated data sets we show that at late times the 21-cm power spectrum is fairly insensitive to the details of the reionization process but that the properties of the neutral islands can distinguish between different reionization scenarios. We compare the properties of these islands with those of ionized bubbles. At equivalent volume filling fractions, neutral islands tend to be fewer in number but larger compared to the ionized bubbles. In addition, the evolution of the size distribution of neutral islands is found to be slower than that of the ionized bubbles and also their percolation behaviour differs substantially. Even though the neutral islands are relatively rare, they will be easier to identify in observations with the low frequency component of the Square Kilometre Array (SKA-Low) due to their larger size and the lower noise levels at lower redshifts. The size distribution of neutral islands at the late stages of reionization is found to depend on the source properties, such as the ionizing efficiency of the sources and their minimum mass. We find the longest line of sight through a neutral region to be more than 100 comoving Mpc until very late stages (90-95 per cent reionized), which may have relevance for the long absorption trough at z = 5.6 − 5.8 in the spectrum of quasar ULAS J0148+0600.

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Section: Summary and Discussioncontrasting

confidence: 64%

Neutral island statistics during reionization from 21-cm tomography

Giri

Mellema

Aldheimer

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Planck Collaboration et al 2020;Becker et al 2015;Qin et al 2021a;Becker et al 2021;Bosman et al 2021), with potential neutral islands lasting up to below redshift 6 (Kulkarni et al 2019;Keating et al xuyd@nao.cas.cn (YX), zhangxin@mail.neu.edu.cn (XZ), xuelei@cosmology.bao.ac.cn (XC) 2020). Increasing attention has been driven to the late EoR, investigating the statistics of the large-scale neutral regions (islands) (Giri et al 2019;Nasir & D'Aloisio 2020), how the islands evolves (Xu et al 2014(Xu et al , 2017, and a statistical tool has been proposed to determine the completing redshift of reionization by measuring the 21-cm bias (Xu et al 2019).…”

Section: Introductionmentioning

confidence: 99%

“…These played a significant role in regulating the ionizing background and the reionization process (e.g. Miralda-Escudé et al 2000;Alvarez & Abel 2012;Xu et al 2017). Therefore, it is essential to properly model the effects of SSAs when predicting and interpreting the upcoming 21-cm data, especially for the signal from the late EoR (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Iliev et al (2007) for full-numerical simulations, and Sobacchi & Mesinger (2014) for semi-numerical simulations), or by introducing a MFP parameter (see, e.g. Iliev et al (2014); Shukla et al (2016) for full-numerical simulations, and Alvarez & Abel (2012); Xu et al (2017) for semi-numerical simulations). In particular, Alvarez & Abel (2012) used a semi-numerical approach to investigate the effect of the abundance of SSAs on the largescale morphology and the overall progress of reionization, by varying the MFP parameter, and found that the characteristic bubble size is quite sensitive to the MFP of ionizing photons.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Small-Scale Absorption Systems on Neutral Islands during the Late Epoch of Reionization

Wu,

Xu,

Zhang

et al. 2021

Preprint

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The reionization process is expected to be prolonged by the small-scale absorbers (SSAs) of ionizing photons, which have been seen as Lyman-limit systems in quasar absorption line observations. We use a set of semi-numerical simulations to investigate the effects of absorption systems on the reionization process, especially their impacts on the neutral islands during the late Epoch of Reionization (EoR). Three model are studied, i.e. the extreme case of no-SSA model with a high level of ionizing background, the moderate-SSA model with a relatively high level of ionizing background, and the dense-SSA model with a low level of ionizing background. We find that while the characteristic scale of neutral regions decreases during the early and middle stages of reionization, it stays nearly unchanged at about 10 comoving Mpc during the late stage for the no-SSA and moderate-SSA models. However, in the case of weak ionizing background in the dense-SSA model, the characteristic island scale shows obvious evolution, as large islands break into many small ones that are slowly ionized. The evolutionary behavior of neutral islands during the late EoR thus provides a novel way to constrain the abundance of SSAs. We discuss the 21-cm observation with the upcoming Square Kilometre Array (SKA). The different models can be distinguished by the 21-cm power spectrum measurement, and it is also possible to extract the characteristic island scale from the imaging observation with a proper choice of the 21-cm brightness threshold.

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“…There are several key differences between their work and ours. For these late stages of reionization, they use the code FAST (Xu et al 2017) and their MFP parameter is not constant but has a redshift dependence according to the fit from Songaila & Cowie (2010). Furthermore, they included a contribution from H in galaxies in their bias parameter.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

The large-scale 21-cm power spectrum from reionization

Georgiev,

Mellema,

Giri

et al. 2021

Preprint

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Radio interferometers, such as the Low-Frequency Array (LOFAR) and the future Square Kilometre Array (SKA), are attempting to measure the spherically averaged 21-cm power spectrum from the Epoch of Reionization (EoR). Understanding of the dominant physical processes which influence the power spectrum at each length-scale is therefore crucial for interpreting any future detection. We study a decomposition of the 21-cm power spectrum and quantify the evolution of its constituent terms for a set of numerical and semi-numerical simulations of a volume of (714 Mpc) 3 , focusing on large scales with 𝑘 0.3 Mpc −1 After ∼ 10 per cent of the Universe has been ionized, the 21-cm power spectrum follows the power spectrum of neutral hydrogen fluctuations, which itself beyond a certain scale follows the matter power spectrum. Hence the signal has a two-regime form where the large-scale signal is a biased version of the cosmological density field, and the small-scale power spectrum is determined by the astrophysics of reionization. We construct a bias parameter to investigate which 𝑘-scales of the large-scale 21-cm signal can be utilised as a probe of cosmology. We find that the transition scale between the scale-independent and scale-dependent bias regimes is directly related to the value of the mean free path of ionizing photons (𝜆 MFP ), and is characterised by the empirical formula 𝑘 trans ≈ 2/𝜆 MFP . Furthermore, we show that the numerical implementation of the mean free path effect has a significant impact on the shape of this transition. Most notably, the transition is more gradual if the mean free path effect is implemented as an absorption process rather than as a barrier.

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IslandFAST: A Semi-numerical Tool for Simulating the Late Epoch of Reionization

Cited by 18 publications

References 63 publications

Neutral island statistics during reionization from 21-cm tomography

Neutral island statistics during reionization from 21-cm tomography

Effects of Small-Scale Absorption Systems on Neutral Islands during the Late Epoch of Reionization

The large-scale 21-cm power spectrum from reionization

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