A survey of Low Luminosity Compact sources and its implication for evolution of radio-loud AGNs. II. Optical analysis

TL;DR

This paper analyzes the optical properties of low luminosity compact radio sources, comparing them with other radio galaxy types, and proposes parallel evolutionary tracks for high and low excitation galaxies based on optical and radio data.

Contribution

It provides a comprehensive optical analysis of LLC sources, classifies them into HEG and LEG, and suggests independent, parallel evolution paths for these classes.

Findings

LLC sources have lower [OIII] luminosity than brighter CSS sources.

HEG and LEG follow separate, parallel evolutionary tracks.

LLC and luminous CSS behave like FRII sources in ionization mechanisms.

Abstract

This is the second in a series of papers concerning a new sample of low luminosity compact (LLC) objects. Here we discuss the optical properties of the sample based on Sloan Digital Sky Survey (SDSS) images and spectra. We have generated different diagnostic diagrams and classified the sources as high and low excitation galaxies (HEG and LEG, respectively). We have studied the jet-host interactions, relation between radio and optical line emission and evolution of the radio source within a larger sample that included also the published samples of compact steep spectrum (CSS), gigahertz peaked spectrum (GPS) sources and FRII and FRI objects. The optical and radio properties of the LLC sample are in general consistent with brighter CSS and large-scale radio sources, although the LLC objects have lower values of [OIII] luminosity than the more powerful CSS sources (L_1.4GHz>10^25 W/Hz). However, when LLC are added to the other samples, HEG and LEG seem to follow independent, parallel evolutionary tracks. Regarding ionization mechanisms, LLC and luminous CSS objects behave like FRII sources, while FRI seem to belong to a different group of objects. Based on our results, we propose the independent, parallel evolutionary tracks for HEG and LEG sources, evolving from GPS - CSS - FR.