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Bubble size statistics during reionization from 21-cm tomography
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Number of Authors: 4
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 473, no 3, p. 2949-2964Article in journal (Refereed) Published
Abstract [en]

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 (Delta z similar to 0.5). We find that RSDs only marginally affect the bubble size distributions.

Place, publisher, year, edition, pages
2018. Vol. 473, no 3, p. 2949-2964
Keyword [en]
methods: statistical, techniques: image processing, dark ages, reionization, first, stars, early Universe, radio lines: galaxies
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-153886DOI: 10.1093/mnras/stx2539ISI: 000423809400007OAI: oai:DiVA.org:su-153886DiVA, id: diva2:1188396
Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-03-07Bibliographically approved

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Giri, Sambit K.Mellema, Garrelt
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Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)
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Astronomy, Astrophysics and Cosmology

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