Modifications to the Cosmic 21-cm Background Frequency Spectrum by Scattering via electrons in Galaxy Clusters

Abstract

The cosmic 21-cm background frequency spectrum related to the spin-flip transition of neutral Hydrogen present during and before the era of reionization is rich in features associated with physical processes that govern transitions between the two spin states. The intervening electrons in foreground galaxy clusters inversely Compton scatter the 21-cm background spectrum and modify it just as the cosmic microwave background (CMB) spectrum is modified by inverse-Compton scattering. Towards typical galaxy clusters at low redshifts, the resulting modification is a few tenths milli-Kelvin correction to the few tens milli-Kelvin temperature of 21-cm signal relative to that of the cosmic microwave background black body spectrum. The modifications are mostly associated with sharp changes in the cosmic 21-cm background spectrum such as due to the onset of a Lyman-$\alpha$ radiation field or heating of neutral gas. Though low frequency radio interferometers that are now planned for 21-cm anisotropy measurements are insensitive to the mean 21-cm spectrum, differential observations of galaxy clusters with these interferometers can be utilized to indirectly establish global features in the 21-cm frequency spectrum. We discuss the feasibility to detect the spectrum modified by clusters and find that for upcoming interferometers, while a detection towards an individual cluster is challenging, one can average signals over a number of clusters, selected based on the strength of the Sunyave-Zel'dovich effect at high radio frequencies involving CMB scattering alone, to establish the mean 21-cm spectrum.

6 pages, 3 figures, PRD in press; expanded and title changed from v1. Final version in press

References in corpus (9)

• 21 Centimeter Fluctuations from Cosmic Gas at High Redshifts
• Measuring the Small-Scale Power Spectrum of Cosmic Density Fluctuations Through 21 cm Tomography Prior to the Epoch of Structure Formation
• Multifrequency analysis of 21 cm fluctuations from the Era of Reionization
• Detecting the Earliest Galaxies Through Two New Sources of 21cm Fluctuations
• The CMBR fluctuations from HI perturbations prior to reionization
• Nonlinear clustering during the cosmic Dark Ages and its effect on the 21-cm background from minihalos
• Cosmic 21-cm Delensing of Microwave Background Polarization and the Minimum Detectable Energy Scale of Inflation
• Lensing Studies with Diffuse Backgrounds
• Sunyaev-Zel'dovich Cluster Survey Simulations for Planck

Cited by in corpus (12)

• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• The Global 21 Centimeter Background from High Redshifts
• 21 cm fluctuations from inhomogeneous X-ray heating before reionization
• Cosmological and Astrophysical Parameter Measurements with 21-cm Anisotropies During the Era of Reionization
• Refined modelling of the radio SZ signal: kinematic terms, relativistic temperature corrections and anisotropies in the radio background
• Inverse-Compton Scattering of the Cosmic Infrared Background
• Stokes parameters spectral distortions due to the Sunyaev-Zel'dovich effect and an independent estimation of the CMB low multipoles
• The impact of non-Planckian effects on cosmological radio backgrounds
• Polarization of the Sunyaev-Zel'dovich effect: relativistic imprint of thermal and non-thermal plasma
• Probing the physics and history of cosmic reionization with the Sunyaev-Zel'dovich Effect
• Thermal and non-thermal Sunyaev-Zel'dovich effect in the cavities of the galaxy cluster MS 0735.6+7421: the role of the thermal density in the cavity
• Simulated differential observations of the Sunyaev-Zel'dovich Effect: Probing the Dark Ages and Epoch of Reionization