Emission line - radio correlation for Low Luminosity Compact sources. Evolution schemes

TL;DR

This study investigates Low Luminosity Compact (LLC) radio sources, revealing they may be short-lived objects with disrupted emission, and proposes parallel evolutionary tracks for high and low excitation galaxies based on radio and optical properties.

Contribution

It introduces a detailed analysis of LLC sources, suggesting they follow independent, parallel evolutionary paths for HEG and LEG, differing from brighter CSS and large-scale sources.

Findings

LLC sources occupy a distinct space in radio power vs. size diagram.

Many LLCs may be short-lived, with disrupted radio emission.

HEG and LEG follow separate evolutionary tracks from GPS to FR stages.

Abstract

We present radio and optical analysis of a sample of Low Luminosity Compact (LLC) objects, selected from FIRST survey and observed with MERLIN at L-band and C-band. The main criterion used for selection was luminosity of the objects and approximately one third of the CSS sources from the new sample have a value of radio luminosity comparable to FR\,Is.The analysis of a radio properties of LLC sources show they occupy the space in radio power versus linear size diagram below the main evolutionary path of radio objects. We suggest that many of them might be short-lived objects, and their radio emission may be disrupted several times before becoming FR\,IIs. The optical analysis of the LLC sources were made based on the available SDSS images and spectra. We have classified the sources as high and low excitation galaxies (HEG and LEG, respectively). The optical and radio properties of the LLC sample are in general consistent with brighter CSSs and large-scale radio sources. However, when LLC are added to the other samples, HEG and LEG seem to follow independent, parallel evolutionary tracks. LLC and luminous CSS behave like FR\,II sources, while FR\,I seem to belong to a different group of objects, concerning ionization mechanisms. Based on our results, we propose the independent, parallel evolutionary tracks for HEG and LEG sources, evolving from GPS - CSS - FR.