HIR4: Cosmological signatures imprinted on the cross correlation between 21-cm map and galaxy clustering

TL;DR

This paper investigates how cosmological signals are imprinted on the cross-correlation between 21-cm intensity maps and galaxy clustering, accounting for foreground contamination and noise, and forecasts precise distance measurements from these correlations.

Contribution

It introduces a detailed simulation-based analysis of foreground effects on 21-cm and galaxy cross-correlations, demonstrating the robustness of the cross-power spectrum for cosmological measurements.

Findings

Foreground residuals affect HI autocorrelation but not cross-correlation.

Cross-correlation bias is scale-independent and can be modeled.

Forecasts a 2.7% precision in angular diameter distance at z~0.8.

Abstract

We explore the cosmological multitracer synergies between an emission line galaxy distribution from the Dark Energy Spectroscopic Instrument and a Tianlai Project 21-cm intensity map. We use simulated maps generated from a particle simulation in the light-cone volume (Horizon Run 4), sky-trimmed and including the effects of foreground contamination, its removal and instrument noise. We first validate how the foreground residual affects the recovered 21-cm signal by putting different levels of foreground contamination into the 21-cm maps. We find that the contamination cannot be ignored in the angular autocorrelation power spectra of HI even when it is small, but has no influence on the accuracy of the angular cross-power spectra between HI and galaxies. In the foreground-cleaned map case, as information is lost in the cleaning procedure, there is also a bias in the cross-correlation power spectrum. However, we found that the bias from the cross-correlation power spectrum is scale-independent, which is easily parameterized as part of the model, while the offset in the HI autocorrelation power spectrum is non-linear. In particular, we tested that the cross-correlation power also benefits from the cancellation of the bias in the power spectrum measurement that is induced by the instrument noise, which changes the shape of the autocorrelation power spectra but leaves the cross-correlation power unaffected. We then modelled the angular cross-correlation power spectra to fit the baryon acoustic oscillation feature in the broad-band shape of the angular cross-correlation power spectrum, including contamination from the residual foreground and the effect of instrument noise. We forecast a constraint on the angular diameter distance $D_\mathrm{A}$ for the Tianlai Pathfinder redshift $0.775<z<1.03$, giving a distance measurement with a precision of 2.7\% at that redshift.