FIRST-based survey of Compact Steep Spectrum sources, V. Milliarcsecond-scale morphology of CSS objects

TL;DR

This paper presents high-resolution VLBA observations of CSS sources to investigate their morphology, potential intermittent activity, and relation to BAL quasars, revealing complex structures and possible episodic activity in these young radio objects.

Contribution

It provides the first milliarcsecond-scale VLBA imaging of a sample of FIRST-based CSS sources, highlighting complex morphologies and evidence of intermittent activity, especially in the BAL quasar 1045+352.

Findings

Some sources show complex, possibly episodic radio morphologies.

1045+352 is a young, asymmetric CSS quasar with signs of intermittent activity.

Submillimetre flux in 1045+352 may be contaminated by synchrotron emission.

Abstract

Multifrequency VLBA observations of the final group of ten objects in a sample of FIRST-based compact steep spectrum (CSS) sources are presented. The sample was selected to investigate whether objects of this kind could be relics of radio-loud AGNs switched off at very early stages of their evolution or possibly to indicate intermittent activity. Initial observations were made using MERLIN at 5 GHz. The sources have now been observed with the VLBA at 1.7, 5 and 8.4 GHz in a snapshot mode with phase-referencing. The resulting maps are presented along with unpublished 8.4-GHz VLA images of five sources. Some of the sources discussed here show a complex radio morphology and therefore a complicated past that, in some cases, might indicate intermittent activity. One of the sources studied - 1045+352 - is known as a powerful radio and infrared-luminous broad absorption line (BAL) quasar. It is a young CSS object whose asymmetric two-sided morphology on a scale of several hundred parsecs, extending in two different directions, may suggest intermittent activity. The young age and compact structure of 1045+352 is consistent with the evolution scenario of BAL quasars. It has also been confirmed that the submillimetre flux of 1045+352 can be seriously contaminated by synchrotron emission.