Inevitable imprints of patchy reionization on the cosmic microwave background anisotropy

Abstract

Reionization of the cosmic neutral hydrogen by the first stars in the Universe is an inhomogeneous process which produces spatial fluctuations in free electron density. These fluctuations lead to observable signatures in cosmological probes like the cosmic microwave background (CMB). We explore the effect of the electron density fluctuations on CMB using photon-conserving semi-numerical simulations of reionization named \texttt{SCRIPT}. We show that the amplitude of the kinematic Sunyaev-Zeldovich (kSZ) and $B$-mode polarization signal depends on the patchiness in the spatial distribution of electrons along with the dependence on mid-point and extent of the reionization history. Motivated by this finding, we provide new scaling relations for the amplitude of kSZ and $B$-mode polarization signal which can capture the effects arising from the mean optical depth, width of reionization, and spatial fluctuations in the electron density arising from patchy reionization. We show that the amplitude of the kSZ and $B$-mode polarization signal exhibits different dependency on the width of reionization and the patchiness of reionization, and hence a joint study of these CMB probes will be able to break the degeneracy. By combining external datasets from 21~cm measurements, the degeneracy can be further lifted by directly exploring the sizes of the ionized regions.

16 pages, 11 figures, accepted for publication in MNRAS

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• Constraining the reionization and thermal history of the Universe using a semi-numerical photon-conserving code SCRIPT
• Reconstructing Patchy Reionization with Deep Learning
• Prospects for kSZ${}^2$-Galaxy Cross-Correlations during Reionization
• Reconstructing Cosmic Polarization Rotation with ResUNet-CMB
• Inference of gravitational lensing and patchy reionization with future CMB data
• Joint constraints on reionization: a framework for combining the global 21cm signal and the kinetic Sunyaev-Zel'dovich effect
• A framework to mitigate patchy reionization contamination on the primordial gravitational wave signal
• Reconstructing patchy helium reionization using the cosmic microwave background and large-scale structure
• Modified Cosmology or Modified Galaxy Astrophysics is Driving the z>6 JWST Results? CMB Experiments can discover the Origin in the Near Future
• Revisiting secondary CMB distortions due to kinetic Sunyaev-Zel'dovich effect from quasar bubbles before reionization