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Modelling cosmological reionization and its observational signatures

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posted on 2023-06-10, 00:57 authored by Michele Bianco
The Epoch of Reionization is an important period in studying structure formation and evolution of our Universe. The first luminous objects, which may have been star-forming galaxies and quasi-stellar objects, influenced later-day structures formation and evolution. These bright objects produced enough ultra-violet radiation to alter the nature of the host and propagated out into the intergalactic medium. These energetic photons transitioned our Universe from a cold and neutral state to ultimately a hot and ionised state. This interesting period is one of the least understood epochs in the Universe evolution due to the lack of direct observations. The redshifted 21-cm signal of neutral hydrogen can be used as an observable sign of reionisation. The upcoming Square Kilometre Array telescope will be sensitive enough to detect the 21-cm signal and produce images of its spatial distribution throughout reionisation. This research focuses on improving numerical methods and develop new techniques for understanding and interpreting future observational evidence. Our simulations will play a crucial role and provide numerical support for the upcoming experiments. We proposed a new approach that correctly quantifies the effect of local recombinations on the scale below the large numerical simulation resolution. We present a more general model for the sub-grid gas clumping, depending on the local density. I improved the latter method with an empirical stochastic model based on high-resolution N-body simulation results, and the relevant fluctuations are fully resolved. Moreover, we developed a stable and reliable convolutional neural network, which can identify neutral and ionised regions from noisy 21-cm image observations. The network can identify the regions of interest with greater precision and is less sensitive to the limitation of previous methods. We successfully recover the signal for different instrumental noise levels based on the intensity contrast in the 21-cm signal and from ionised regions simulation independent pattern.

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File Version

  • Published version

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136.0

Department affiliated with

  • Physics and Astronomy Theses

Qualification level

  • doctoral

Qualification name

  • phd

Language

  • eng

Institution

University of Sussex

Full text available

  • Yes

Legacy Posted Date

2021-09-13

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