# 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.

## Key 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 The resulting maps are presented along with unpublished 8.4-GHz VLA images of five sources.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.