Recovering 21-cm signal from simulated FAST intensity maps

TL;DR

This paper demonstrates that PCA-based foreground removal enables accurate recovery of the 21-cm hydrogen signal from simulated FAST telescope data, despite foregrounds and noise.

Contribution

It introduces a model for foregrounds and noise, and shows PCA effectively recovers the HI signal in simulated FAST intensity maps.

Findings

PCA achieves a standard deviation of 0.034 mK between reconstructed and true HI maps.

The HI eigenmode constitutes less than 1% of total sky components.

PCA can accurately recover HI power spectra from simulated FAST data.

Abstract

The 21-cm intensity mapping (IM) of neutral hydrogen (HI) is a promising tool to probe the large-scale structures. Sky maps of 21-cm intensities can be highly contaminated by different foregrounds, such as Galactic synchrotron radiation, free-free emission, extragalactic point sources, and atmospheric noise. We here present a model of foreground components and a method of removal, especially to quantify the potential of Five-hundred-meter Aperture Spherical radio Telescope (FAST) for measuring HI IM. We consider 1-year observational time with the survey area of $20,000\,{\rm deg}^{2}$ to capture significant variations of the foregrounds across both the sky position and angular scales relative to the HI signal. We first simulate the observational sky and then employ the Principal Component Analysis (PCA) foreground separation technique. We show that by including different foregrounds, thermal and $1/f$ noises, the value of the standard deviation between reconstructed 21-cm IM map and the input pure 21-cm signal is $\Delta T = 0.034\,{\rm mK}$, which is well under control. The eigenmode-based analysis shows that the underlying HI eigenmode is just less than $1$ per cent level of the total sky components. By subtracting the PCA cleaned foreground+noise map from the total map, we show that PCA method can recover HI power spectra for FAST with high accuracy.