Synoptic Wide-field EVN--e-MERLIN Public Survey (SWEEPS) -- I. First steps towards commensal surveys with VLBI

TL;DR

The SWEEPS project demonstrates a new commensal VLBI survey mode that can detect faint radio sources over large sky areas, enabling extensive statistical studies of active galactic nuclei and star formation.

Contribution

This paper introduces a novel commensal observing mode for VLBI that increases survey efficiency and source detection capabilities over large sky areas.

Findings

Detected a 5.6 mJy core-jet object at 1.7 GHz using the new method.

First successful detection in the SWEEPS pilot program.

Shows potential for expanding VLBI source samples significantly.

Abstract

The high angular resolution and sensitivity of Very Long Baseline Interferometry (VLBI) offer a unique tool to identify and study active galactic nuclei and star-formation activity over cosmic time. However, despite recent technical advances, such as multiple phase centre correlation, VLBI surveys have thus far been limited to either a few well-studied deep-fields or wide-areas to a relatively shallow depth. To enter the era of extensive statistical studies at high angular resolution, a significantly larger area of the sky must be observed to much better sensitivity with VLBI. The Synoptic Wide-field EVN--e-MERLIN Public Survey (SWEEPS) is a proposed commensal observing mode for the EVN and e-MERLIN, where single-target principle investigator-led observations are re-correlated at the position of known radio sources within 12 arcmin of the pointing centre. Here, we demonstrate a proof-of-concept of this methodology by detecting a 5.6 mJy core-jet object at 1.7 GHz that would have otherwise been lost from the parent data set. This is the first object to be recovered as part of the SWEEPS pilot programme, which highlights the potential for increasing sample sizes of VLBI-detected radio sources with commensal observing modes in the near future.