Engineering topics

Norris, Ray P. (ORCID:0000000245971906)

Publications and source records attributed to Norris, Ray P. (ORCID:0000000245971906).

4 records

DOE OSTI2023

MeerKAT view of the dancing ghosts – peculiar galaxy pair PKS 2130−538 in Abell 3785

ABSTRACT We present MeerKAT L-band (886–1682 MHz) observations of the extended radio structure of the peculiar galaxy pair PKS 2130−538 known as the ‘Dancing Ghosts’. The complex of bending and possibly interacting jets and lobes originate from two active galactic nuclei hosts in the Abell 3785 galaxy cluster, one of which is the brightest cluster galaxy. The radio properties of the PKS 2130−538 – flux density, spectral index, and polarization – are typical for large, bent-tail galaxies. We also investigate a number of thin extended low surface brightness filaments originating from the lobes. South-east from the Dancing Ghosts, we detect a region of low surface brightness emission that has no clear origin. While it could originate from the Abell 3785 radio halo, we investigate the possibility that it is associated with the two PKS 2130−538 hosts. We find no evidence of interaction between the two PKS 2130−538 hosts.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Deep learning for morphological identification of extended radio galaxies using weak labels

Abstract The present work discusses the use of a weakly-supervised deep learning algorithm that reduces the cost of labelling pixel-level masks for complex radio galaxies with multiple components. The algorithm is trained on weak class-level labels of radio galaxies to get class activation maps (CAMs). The CAMs are further refined using an inter-pixel relations network (IRNet) to get instance segmentation masks over radio galaxies and the positions of their infrared hosts. We use data from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, specifically the Evolutionary Map of the Universe (EMU) Pilot Survey, which covered a sky area of 270 square degrees with an RMS sensitivity of 25–35 $\mu$ Jy beam $^{-1}$ . We demonstrate that weakly-supervised deep learning algorithms can achieve high accuracy in predicting pixel-level information, including masks for the extended radio emission encapsulating all galaxy components and the positions of the infrared host galaxies. We evaluate the performance of our method using mean Average Precision (mAP) across multiple classes at a standard intersection over union (IoU) threshold of 0.5. We show that the model achieves a mAP $_{50}$ of 67.5% and 76.8% for radio masks and infrared host positions, respectively. The network architecture can be found at the following link: https://github.com/Nikhel1/Gal-CAM

Astronomy & Astrophysics↗

DOE OSTI2022

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.

Astronomy & Astrophysics↗

DOE OSTI2021

Discovery of a new extragalactic circular radio source with ASKAP: ORC J0102–2450

ABSTRACT We present the discovery of another odd radio circle (ORC) with the Australian Square Kilometre Array Pathfinder (ASKAP) at 944 MHz. The observed radio ring, ORC J0102–2450, has a diameter of ∼70 arcsec or 300 kpc, if associated with the central elliptical galaxy DES J010224.33–245039.5 (z ∼ 0.27). Considering the overall radio morphology (circular ring and core) and lack of ring emission at non-radio wavelengths, we investigate if ORC J0102–2450 could be the relic lobe of a giant radio galaxy seen end on or the result of a giant blast wave. We also explore possible interaction scenarios, for example, with the companion galaxy, DES J010226.15–245104.9, located in or projected on to the south-eastern part of the ring. We encourage the search for further ORCs in radio surveys to study their properties and origin.

Koribalski, Bärbel S. (ORCID:000000034351993X)↗