Predictions for measuring the 21-cm multi-frequency angular power spectrum using SKA-Low

• Published in: arXiv.org 2020-04
• Main Authors: Mondal, Rajesh, Shaw, Abinash Kumar, Iliev, Ilian T, Bharadwaj, Somnath, Datta, Kanan K, Majumdar, Suman, Sarkar, Anjan K, Dixon, Keri L
• Format: Article
• Language: English
• Subjects: Confidence intervals; Ergodic processes; Ionization; Line of sight; Red shift; Spectrum allocation; Statistical analysis
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1910.05196

The light-cone (LC) effect causes the mean as well as the statistical properties of the redshifted 21-cm signal \(T_{\rm b}(\hat{\bf n},\nu)\) to change with frequency \(\nu\) (or cosmic time). Consequently, the statistical homogeneity (ergodicity) of the signal along the line of sight (LoS) direction is broken. This is a severe problem particularly during the Epoch of Reionization (EoR) when the mean neutral hydrogen fraction (\(\bar{x}_{\rm HI}\)) changes rapidly as the universe evolves. This will also pose complications for large bandwidth observations. These effects imply that the 3D power spectrum \(P(k)\) fails to quantify the entire second-order statistics of the signal as it assumes the signal to be ergodic and periodic along the LoS. As a proper alternative to \(P(k)\), we use the multi-frequency angular power spectrum (MAPS) \({\mathcal C}_{\ell}(\nu_1,\nu_2)\) which does not assume the signal to be ergodic and periodic along the LoS. Here, we study the prospects for measuring the EoR 21-cm MAPS using future observations with the upcoming SKA-Low. Ignoring any contribution from the foregrounds, we find that the EoR 21-cm MAPS can be measured at a confidence level \(\ge 5\sigma\) at angular scales \(\ell \sim 1300\) for total observation time \(t_{\rm obs} \ge 128\,{\rm hrs}\) across \(\sim 44\,{\rm MHz}\) observational bandwidth. We also quantitatively address the effects of foregrounds on MAPS detectability forecast by avoiding signal contained within the foreground wedge in \((k_\perp, k_\parallel)\) plane. These results are very relevant for the upcoming large bandwidth EoR experiments as previous predictions were all restricted to individually analyzing the signal over small frequency (or equivalently redshift) intervals.