Radio Galaxy Zoo: New Giant Radio Galaxies in the RGZ DR1catalogue

TL;DR

This paper reports the discovery of five new giant radio galaxies using citizen science data, and discusses their association with galaxy clusters, challenging previous ideas about their growth environments.

Contribution

The study introduces a new selection method for identifying giant radio galaxies and increases the known population of BCG-associated GRGs by over 60%.

Findings

Five new GRGs identified using citizen science data.

Most GRGs are associated with galaxy clusters, not just under-dense regions.

The number of known BCG GRGs has increased significantly.

Abstract

In this paper, we present the identification of five previously unknown giant radio galaxies (GRGs) using Data Release 1 of the Radio Galaxy Zoo citizen science project and a selection method appropriate to the training and validation of deep learning algorithms for new radio surveys. We associate one of these new GRGs with the brightest cluster galaxy (BCG) in the galaxy cluster GMBCG J251.67741+36.45295 and use literature data to identify a further 13 previously known GRGs as BCG candidates, increasing the number of known BCG GRGs by >60%. By examining local galaxy number densities for the number of all known BCG GRGs, we suggest that the existence of this growing number implies that GRGs are able to reside in the centers of rich ($\sim 10^{14}$ M$_{\odot}$) galaxy clusters and challenges the hypothesis that GRGs grow to such sizes only in locally under-dense environments.