Discovery of Peculiar Radio Morphologies with ASKAP using Unsupervised Machine Learning

Abstract

We present a set of peculiar radio sources detected using an unsupervised machine learning method. We use data from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to train a self-organizing map (SOM). The radio maps from three ASKAP surveys, Evolutionary Map of Universe pilot survey (EMU-PS), Deep Investigation of Neutral Gas Origins pilot survey (DINGO) and Survey With ASKAP of GAMA-09 + X-ray (SWAG-X), are used to search for the rarest or unknown radio morphologies. We use an extension of the SOM algorithm that implements rotation and flipping invariance on astronomical sources. The SOM is trained using the images of all "complex" radio sources in the EMU-PS which we define as all sources catalogued as "multi-component". The trained SOM is then used to estimate a similarity score for complex sources in all surveys. We select 0.5\% of the sources that are most complex according to the similarity metric, and visually examine them to find the rarest radio morphologies. Among these, we find two new odd radio circle (ORC) candidates and five other peculiar morphologies. We discuss multiwavelength properties and the optical/infrared counterparts of selected peculiar sources. In addition, we present examples of conventional radio morphologies including: diffuse emission from galaxy clusters, and resolved, bent-tailed, and FR-I and FR-II type radio galaxies. We discuss the overdense environment that may be the reason behind the circular shape of ORC candidates.

Accepted in PASA, 23 pages, 16 figures

References in corpus (18)

• Diffuse Radio Emission from Galaxy Clusters
• Galaxy Groups within 3500 km s${}^{-1}$
• Calibration of the optical mass proxy for clusters of galaxies and an update of the WHL12 cluster catalog
• Brightest Cluster Galaxies at the Present Epoch
• Radio Sources Toward Galaxy Clusters at 30 GHz
• A catalogue of clusters of galaxies identified from all sky surveys of 2MASS, WISE, and SuperCOSMOS
• Two New Catalogues of Superclusters of Abell/ACO Galaxy Clusters out to redshift 0.15
• Galaxy Clusters from the DESI Legacy Imaging Surveys. I. Cluster Detection
• Cataloging the radio-sky with unsupervised machine learning: a new approach for the SKA era
• Unveiling the rarest morphologies of the LOFAR Two-metre Sky Survey radio source population with self-organised maps
• Head-Tail Galaxies: Beacons of High-Density Regions in Clusters
• The FIR-Radio Relationship at High and Low Redshift
• Where are compact groups in the local Universe?
• Odd Radio Circles and their Environment
• Morphological classification of compact and extended radio galaxies using convolutional neural networks and data augmentation techniques
• Fokker-Planck Models for M15 without a Central Black Hole: The Role of the Mass Function
• Diffuse Radio Sources in a Statistically Complete Sample of High Redshift Galaxy Clusters
• Measurements of the Hyperfine Structure of Atomic Energy Levels in Co II

Cited by in corpus (2)

• A review of unsupervised learning in astronomy
• Single- and double-headed odd radio circles in the LOFAR surveys