Spurious source generation in mapping from noisy phase-self-calibrated data

TL;DR

This paper investigates how phase self-calibration in interferometry can produce false sources from noise, providing analytical insights and tests to distinguish real signals from artifacts.

Contribution

It reveals the conditions under which selfcal generates spurious sources from noise and offers practical tests to identify genuine astronomical signals.

Findings

Spurious sources can be generated from pure noise by selfcal.

The maximum spurious flux density depends on observation parameters.

Two simple tests can distinguish real sources from artifacts.

Abstract

Phase self-calibration (or selfcal) is an algorithm often used in the calibration of interferometric observations in astronomy. Although a powerful tool, this algorithm presents strong limitations when applied to data with a low signal-to-noise ratio. We analyze the artifacts that the phase selfcal algorithm produces when applied to extremely noisy data. We show how the phase selfcal may generate a spurious source in the sky from a distribution of completely random visibilities. This spurious source is indistinguishable from a real one. We numerically and analytically compute the relationship between the maximum spurious flux density generated by selfcal from noise and the particulars of the interferometric observations. Finally, we present two simple tests that can be applied to interferometric data for checking whether a source detection is real or whether the source is an artifact of the phase self-calibration algorithm.