The shape and size distribution of H II regions near the percolation transition

Bag, Satadru, Mondal, Rajesh, Sarkar, Prakash, Bharadwaj, Somnath and Sahni, Varun (2018) The shape and size distribution of H II regions near the percolation transition. Monthly Notices of the Royal Astronomical Society, 477 (2). pp. 1984-1992. ISSN 0035-8711

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Using Shapefinders, which are ratios of Minkowski functionals, we study the morphology of neutral hydrogen (H I) density fields, simulated using seminumerical technique (inside-out), at various stages of reionization. Accompanying the Shapefinders, we also employ the ‘largest cluster statistic’ (LCS), originally proposed in Klypin & Shandarin, to study the percolation in both neutral and ionized hydrogen. We find that the largest ionized region is percolating below the neutral fraction xHI≲0.728 (or equivalently z ≲ 9). The study of Shapefinders reveals that the largest ionized region starts to become highly filamentary with non-trivial topology near the percolation transition. During the percolation transition, the first two Shapefinders – ‘thickness’ (T) and ‘breadth’ (B) – of the largest ionized region do not vary much, while the third Shapefinder – ‘length’ (L) – abruptly increases. Consequently, the largest ionized region tends to be highly filamentary and topologically quite complex. The product of the first two Shapefinders, T × B, provides a measure of the ‘cross-section’ of a filament-like ionized region. We find that, near percolation, the value of T × B for the largest ionized region remains stable at ∼7 Mpc2 (in comoving scale) while its length increases with time. Interestingly, all large ionized regions have similar cross-sections. However, their length shows a power-law dependence on their volume, L ∝ V0.72, at the onset of percolation.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Depositing User: Rajesh Mondal
Date Deposited: 19 Jun 2019 11:53
Last Modified: 01 Jul 2019 12:16

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