An Evolutionary Sequence of Young Radio Galaxies

TL;DR

This study investigates the evolutionary stages of young radio galaxies by analyzing their radio morphologies, sizes, and other age indicators, providing insights into their development and accretion modes.

Contribution

It presents high-resolution radio observations of faint GPS and CSS sources, establishing their evolutionary sequence and linking radio morphology with other age indicators.

Findings

GPS/CSS sources are confirmed as young, evolving radio galaxies.

Linear size correlates with evolutionary stage.

Evidence of changing accretion modes and star formation relationships.

Abstract

We have observed the faintest sample of Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources to date, using the Australia Telescope Compact Array. We test the hypothesis that GPS and CSS sources are the youngest radio galaxies, place them into an evolutionary sequence along with a number of other young Active Galactic Nuclei (AGN) candidates, and search for evidence of the evolving accretion mode and its relationship to star formation. GPS/CSS sources have very small radio jets that have been recently launched from the central Supermassive Black Hole and grow in linear size as they evolve, which means that the linear size of the jets is an excellent indicator of the evolutionary stage of the AGN. We use high-resolution radio observations to determine the linear size of GPS/CSS sources, resolve their jets and observe their small-scale morphologies. We combine this with other multi-wavelength age indicators, including the spectral age, colours, optical spectra and Spectral Energy Distribution of the host galaxy, in an attempt to assemble all age indicators into a self-consistent model. We observe the most compact sources with Very Large Baseline Interferometry, which reveals their parsec-scale structures, giving us a range of source sizes and allowing us to test what fraction of GPS/CSS sources are young and evolving.