Compactness of Weak Radio Sources at High Frequencies

TL;DR

This study uses 8.4 GHz VLBA observations to analyze the size, spectra, and suitability of weak high-frequency radio sources as calibrators, aiding in VLBI and array design.

Contribution

It provides new high-resolution measurements of weak radio sources at 8.4 GHz, assessing their compactness and potential as VLBI calibrators.

Findings

Majority of sources have compact <1 mas cores

Large fraction of sources detected with VLBI

Sources exhibit steep radio spectra

Abstract

We have obtained 8.4 GHz VLBA observations of a 31-GHz complete sample of ~100 sources between 10 and 100 mJy. The main goals of these observations are: to determine the angular size, radio spectra and identification for a weak sample of high frequency sources; to find the fraction of sources which have sufficiently compact emission for use as calibrators for VLBI observations; and for design considerations of the proposed DSN Array. We find that a large fraction of observed sources have VLBI detections. A majority of these sources have most of their emission in a compact <1 mas radio core, with remaining sources having steep radio spectra. The source list was provided from GBT observations to remove discrete sources in the CBI fields.