The monopole and quadrupole moments of the epoch of reionization (EoR) 21-cm bispectrum
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY（2024）
摘要
We study the monopole (B(0)(0)) and quadrupole (B(0)(2)) moments of the 21-cm bispectrum (BS) from EoR simulations and present results for squeezed and stretched triangles. Both B(0)(0) and B(0)(2) are positive at the early stage of EoR where the mean neutral hydrogen (HI) density fraction X(HI )approximate to 0.99. The subsequent evolution of B(0)(0) and B(0)(2) at large and intermediate scales (k = 0.29 and 0.56Mpc-1, respectively) is punctuated by two sign changes which mark transitions in the HI distribution. The first sign flip where B(0)(0) becomes negative occurs in the intermediate stages of EoR (X(HI )> 0.5), at large scale first followed by the intermediate scale. This marks the emergence of distinct ionized bubbles in the neutral background. B(0)(2) is relatively less affected by this transition, and it mostly remains positive even when B(0)(0) becomes negative. The second sign flip, which affects both B(0)(0) and B(0)(2), occurs at the late stage of EoR (X(HI )> 0.5). This marks a transition in the topology of the HI distribution, after which we have distinct HI islands in an ionized background. This causes B(0)(0) to become positive. The negative B(0)(2) is a definite indication that the HI islands survive only in underdense regions.
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关键词
methods: statistical,software: simulations,dark ages, reionization, first stars,diffuse radiation
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