The Tianlai Dish Pathfinder Array: design, operation and performance of a prototype transit radio interferometer

TL;DR

The Tianlai Dish Pathfinder Array is a prototype radio interferometer designed for 21cm intensity mapping, demonstrating stable operation, accurate beam patterns, and noise performance suitable for large-scale cosmic structure measurements.

Contribution

This paper presents the design, calibration, and performance analysis of the Tianlai Dish Pathfinder Array as a novel prototype for 21cm intensity mapping.

Findings

Beam patterns agree with simulations and are validated by drone and source transit data.

System temperature is below 80 K for most feeds, with noise decreasing as expected.

Visibilities from long integrations match the expected cosmic signal with high precision.

Abstract

The Tianlai Dish Pathfinder Array is a radio interferometer designed to test techniques for 21~cm intensity mapping in the post-reionization universe as a means for measuring large-scale cosmic structure. It performs drift scans of the sky at constant declination. We describe the design, calibration, noise level, and stability of this instrument based on the analysis of about $\sim 5 \%$ of 6,200 hours of on-sky observations through October, 2019. Beam pattern determinations using drones and the transit of bright sources are in good agreement, and compatible with electromagnetic simulations. Combining all the baselines, we make maps around bright sources and show that the array behaves as expected. A few hundred hours of observations at different declinations have been used to study the array geometry and pointing imperfections, as well as the instrument noise behaviour. We show that the system temperature is below 80~K for most feed antennas, and that noise fluctuations decrease as expected with integration time, at least up to a few hundred seconds. Analysis of long integrations, from 10 nights of observations of the North Celestial Pole, yielded visibilities with amplitudes of 20-30~mK, consistent with the expected signal from the NCP radio sky with $<10\,$mK precision for $1 ~\mathrm{MHz} \times 1~ \mathrm{min}$ binning. Hi-pass filtering the spectra to remove smooth spectrum signal yields a residual consistent with zero signal at the $0.5\,$mK level.