Bubble size statistics during reionization from 21-cm tomography

Giri, Sambit K, Mellema, Garrelt, Dixon, Keri L and Iliev, Ilian T (2017) Bubble size statistics during reionization from 21-cm tomography. Monthly Notices of the Royal Astronomical Society, 473 (3). pp. 2949-2964. ISSN 0035-8711

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Abstract

The upcoming SKA1-Low radio interferometer will be sensitive enough to produce tomographic imaging data of the redshifted 21-cm signal from the Epoch of Reionization. Due to the non-Gaussian distribution of the signal, a power spectrum analysis alone will not provide a complete description of its properties. Here, we consider an additional metric which could be derived from tomographic imaging data, namely the bubble size distribution of ionized regions. We study three methods that have previously been used to characterize bubble size distributions in simulation data for the hydrogen ionization fraction – the spherical-average (SPA), mean-free-path (MFP) and friends-of-friends (FOF) methods – and apply them to simulated 21-cm data cubes. Our simulated data cubes have the (sensitivity-dictated) resolution expected for the SKA1-Low reionization experiment and we study the impact of both the light-cone (LC) and redshift space distortion (RSD) effects. To identify ionized regions in the 21-cm data we introduce a new, self-adjusting thresholding approach based on the K-Means algorithm. We find that the fraction of ionized cells identified in this way consistently falls below the mean volume-averaged ionized fraction. From a comparison of the three bubble size methods, we conclude that all three methods are useful, but that the MFP method performs best in terms of tracking the progress of reionization and separating different reionization scenarios. The LC effect is found to affect data spanning more than about 10 MHz in frequency (Δz ∼ 0.5). We find that RSDs only marginally affect the bubble size distributions.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy
Depositing User: Billy Wichaidit
Date Deposited: 06 Jun 2018 15:15
Last Modified: 07 Jun 2018 10:57
URI: http://srodev.sussex.ac.uk/id/eprint/76367

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Project NameSussex Project NumberFunderFunder Ref
Astronomy rolling grantG0278STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/I000976/1
UnsetUnsetSTFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/P000252/1