Signatures of cosmic reionization on the 21-cm two- and three-point correlation function I: quadratic bias modelling

• Published in: Monthly notices of the Royal Astronomical Society Vol. 487; no. 3; pp. 3050 - 3068
• Main Authors: Hoffmann, Kai, Mao, Yi, Xu, Jiachuan, Mo, Houjun, Wandelt, Benjamin D
• Format: Journal Article
• Language: English
• Published: Oxford University Press 11.08.2019; Oxford University Press (OUP): Policy P - Oxford Open Option A
• Subjects: Astrophysics; Physics; methods: analytical; methods: statistical; methods: numerical; dark ages, reionization, first stars; reionization; dark ages; first stars
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stz1472

ABSTRACT The three-point correlation function (3PCF) of the 21-cm brightness temperature from the Epoch of Reionization (EoR) probes complementary information to the commonly studied two-point correlation function (2PCF) about the morphology of ionized regions. We investigate the 21-cm 2PCF and 3PCF in configuration space using seminumerical simulations and test whether they can be described by the local quadratic bias model. We find that fits of bias model predictions for the 2PCF and 3PCF deviate from our measurements by ${\sim } 20{{\ \rm per\ cent}}$ at scales above the typical size of ionized regions (≃ 30 Mpc) and at early times with global neutral fractions of $\langle x_{\rm H\, \small {I}} \rangle \gtrsim 0.7$. At later times and smaller scales, these deviations increase strongly, indicating a break-down of the bias model. The 2PCF and 3PCF fits of the linear bias parameter agree at the $10{{\ \rm per\ cent}}$ level for different EoR model configurations. This agreement holds, when adding redshift space distortions to the simulations. The relation between spatial fluctuations in the matter density and the 21-cm signal, as predicted by the bias model, is consistent with direct measurements of this relation in simulations for large smoothing scales (≳30 Mpc). From this latter test, we conclude that negative amplitudes of the 21-cm 3PCF result from negative bias parameters, which describe the anticorrelation between the matter over-densities and the 21-cm signal during the EoR. However, a more detailed interpretation of the bias parameters may require a description of non-local contributions to the bias model.