Predictions for measuring the cross power spectrum of the HI 21-cm signal and the Lyman-$\alpha$ forest using OWFA

TL;DR

This study explores the feasibility of measuring the cross-correlation between the HI 21-cm signal and the Lyman-alpha forest using OWFA, demonstrating potential detection capabilities and parameter measurements at specific redshifts and bandwidths.

Contribution

It provides the first detailed analysis of cross-correlation detection prospects between HI 21-cm and Lyman-alpha forest with OWFA, including optimal observational strategies and expected signal-to-noise ratios.

Findings

6 sigma detection possible at z=3.35 with 200 hrs observation

Enhanced SNR of ~17 at z=2.55 with larger bandwidth

Measurement of bias parameters with SNR ≥ 5

Abstract

We have studied the possibility of measuring the cross-correlation of the redshifted HI 21-cm signal and the Lyman-$\alpha$ forest using an upcoming radio-interferometric array OWFA and an spectroscopic observation like SDSS-IV. Our results shows that it is possible to have a $6 \sigma$ detection of the cross-correlation signal with OWFA PII using an observing time of $200$ hrs each in $N_p = 25$ independent fields-of-view. However, not much can be done beyond this using the cross-correlation signal for $z_c = 3.35$ and $B = 30 \, {\rm MHz}$. Apart from this, we have also envisaged a situation where observations are carried out at $z_c = 3.05$ and $2.55$ which lie closer to the peak of the quasar distribution at $z = 2.25$ and with a larger bandwidth of $B = 60 \, {\rm MHz}$. We see that the SNR of the cross-correlation detection can be significantly enhanced to $\sim 17$ for $z_c = 2.55$ and $B = 60 \, {\rm MHz}$. It is then possible to measure $\beta_T$ and $\beta_F$ individually with an ${\rm SNR} \ge 5$ by combining the cross-correlation with the HI 21-cm auto-correlation measurements. We further find that a measurement of the binned cross-correlation power spectrum with ${\rm SNR} \ge 5$ is also possible in several bins at $k \le 0.3 \, {\rm Mpc}^{-1}$.