Dipole of the Epoch of Reionization 21-cm signal

Abstract

The motion of the solar system with respect to the cosmic rest frame modulates the monopole of the Epoch of Reionization 21-cm signal into a dipole. This dipole has a characteristic frequency dependence that is dominated by the frequency derivative of the monopole signal. We argue that although the signal is weaker by a factor of $\sim 100$, there are significant benefits in measuring the dipole. Most importantly, the direction of the cosmic velocity vector is known exquisitely well from the cosmic microwave background and is not aligned with the galaxy velocity vector that modulates the foreground monopole. Moreover, an experiment designed to measure a dipole can rely on differencing patches of the sky rather than making an absolute signal measurement, which helps with some systematic effects.

4 pages, minor changes, matches version accepted by PRL

References in corpus (2)

• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Erasing the variable: Empirical foreground discovery for global 21 cm spectrum experiments

Cited by in corpus (8)

• Data Analysis for Precision 21 cm Cosmology
• Formulating and critically examining the assumptions of global 21-cm signal analyses: How to avoid the false troughs that can appear in single spectrum fits
• Dipole Anisotropy as an Essential Qualifier for the Monopole Component of the Cosmic-Dawn Spectral Signature, and the Potential of Diurnal Pattern for Foreground Estimation
• Simulation-Based Inference of the sky-averaged 21-cm signal from CD-EoR with REACH
• Effects of observer peculiar motion on the isotropic background frequency spectrum: from monopole to higher multipoles
• Matter Dipole and Hubble Tension due to Large Wavelength Perturbations
• Predictions for the diffuse cosmic dipole at radio frequencies from reionization imprints
• Galaxy number-count dipole and superhorizon fluctuations