Potential Targets for ASTRO-G In-Beam Phase-Referencing

TL;DR

This paper identifies approximately 50 potential in-beam phase-reference quasars for ASTRO-G, most of which are weak and previously un-imaged with VLBI, enabling detailed radio structure studies.

Contribution

It presents an efficient method to pre-select weak VLBI target quasars using optical and low-res radio data, expanding potential calibration sources for ASTRO-G.

Findings

Up to 50 candidate quasars identified within 12' of strong calibrators.

Most candidates have not been previously imaged with VLBI.

The selected sources enable high-resolution statistical studies of weak quasars.

Abstract

We show that as many as ~50 quasars with at least mJy-level expected flux density can be pre-selected as potential in-beam phase-reference targets for ASTRO-G. Most of them have never been imaged with VLBI. These sources are located around strong, compact calibrator sources that have correlated flux density >100 mJy on the longest VLBA baselines at 8.4 GHz. All the targets lie within 12' from the respective reference source. The basis of this selection is an efficient method to identify potential weak VLBI target quasars simply using optical and low-resolution radio catalogue data. The sample of these dominantly weak sources offers a good opportunity for a statistical study of their radio structure with unprecedented angular resolution at 8.4 GHz.