Redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn

Hannah E Ross,Keri L Dixon,Garrelt Mellema,Ilian T Iliev,Raghunath Ghara,Sambit K Giri

doi:10.1093/mnras/stab1822

Abstract

ABSTRACT The 21-cm signal from the Cosmic Dawn (CD) is likely to contain large fluctuations, with the most extreme astrophysical models on the verge of being ruled out by observations from radio interferometers. It is therefore vital that we understand not only the astrophysical processes governing this signal, but also other inherent processes impacting the signal itself, and in particular line-of-sight effects. Using our suite of fully numerical radiative transfer simulations, we investigate the impact on the redshifted 21-cm from the CD from one of these processes, namely the redshift-space distortions (RSDs). When RSDs are added, the resulting boost to the power spectra makes the signal more or equally detectable for our models for all redshifts, further strengthening hopes that a power spectra measurement of the CD will be possible. RSDs lead to anisotropy in the signal at the beginning and end of the CD, but not while X-ray heating is underway. The inclusion of RSDs, however, decreases detectability of the non-Gaussianity of fluctuations from inhomogeneous X-ray heating as measured by the skewness and kurtosis. On the other hand, mock observations created from all our simulations that include telescope noise corresponding to 1000 h of observation with the Square Kilometre Array telescope show that we may be able to image the CD for all heating models considered and suggest RSDs dramatically boost fluctuations coming from the inhomogeneous Ly α background.

Highlights

The Epoch of Reionization (EoR) is constrained to have occurred between z ∼ 5.5 and 15 by observations of both the cosmic microwave background (CMB) (e.g. Komatsu et al 2011; Planck Collaboration 2016) and the Ly-α forest in high redshift quasar spectra (e.g. Fan et al 2005, 2006; Davies et al 2018; Bosman et al 2018; Keating et al 2019)
We showed the differences between our different astrophysical models with the inclusion of redshift-space distortions (RSDs) and demonstrated that they remain distinguishable and detectable
The ratio of ∆221 on large scales matched the amplification factor of 1.87 expected for the matter power spectra (Mao et al 2012), but decreased as the simulation continued. This behaviour is somewhat similar to that found in Jensen et al (2013), with the boost from RSDs decreasing as the magnitude of the 21-cm signal from the densest points decreased

Summary

Introduction

The EoR is constrained to have occurred between z ∼ 5.5 and 15 by observations of both the CMB (e.g. Komatsu et al 2011; Planck Collaboration 2016) and the Ly-α forest in high redshift quasar spectra (e.g. Fan et al 2005, 2006; Davies et al 2018; Bosman et al 2018; Keating et al 2019). Radio telescopes are currently searching for these redshifted 21-cm photons, an extremely. Current radio telescopes capable of detecting the 21-cm signal include the Giant Metrewave Radio Telescope (GMRT)1(Paciga et al 2013), the Low Frequency Array (LOFAR) (van Haarlem et al 2013), the Murchison Widefield Array (MWA) (Bowman et al 2013) and the Hydrogen Epoch of Reionization Array (HERA) (DeBoer et al 2017). These radio interfermometers are sensitive to the fluctuations in the signal rather than its magnitude. The low frequency component of SKA (SKA-Low) will be sensitive enough to detect the power spectrum of the 21-cm signal during CD/EoR and produce images

Methods

Results

Conclusion