EMU and the DRAGNs I: A Catalogue of DRAGNs

TL;DR

This work delivers a comprehensive DRAGN catalogue from the EMU-PS1 field (3557 DRAGNs over ~270 deg$^2$ at 944 MHz) identified by morphology-driven eye inspection and tagged with a flexible, survey-specific taxonomy. It combines radio data with infrared host identifications (WISE/CATWISE2020) and introduces rigorous FR1/FR2 classification via defined geometric metrics, alongside a suite of rare and complex morphologies (HyMoRS, LTS, OSS, BT/HT, XRG/ZRG/TRG, WTF, DD). The catalogue serves as a high-quality ground-truth resource for training ML and citizen-science classifications, and it sets the stage for subsequent papers to explore jet physics, environmental interactions, cluster associations, and spectral properties, while transparently addressing biases and completeness. By comparing EMU DRAGNs with other surveys, the study highlights how observational depth, resolution, and frequency shape the detected DRAGN population, with implications for understanding AGN evolution and the FR dichotomy in the low-to-intermediate luminosity regime.

Abstract

We present a catalogue of 3557 Double Radio sources associated with Active Galactic Nuclei (DRAGNs) from the First Pilot Survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, covering 270 deg^2. We have extracted and identified each source by eye, tagged it with a morphological type and measured its parameters. The resulting catalogue will be used in subsequent papers to explore the properties of these sources, to train machine-learning algorithms for the detection of these sources in larger fields, and to compare with the results of Citizen Science projects, with the ultimate goal of understanding the physical processes that drive DRAGNs. Compared with earlier, lower sensitivity, catalogues, we find more diffuse structure and a plethora of more complex structures, ranging from wings of radio emission on the side of the jets, to types of object which have not been seen in earlier observations. As well as the well-known FR1 and FR2 sources, we find significant numbers of rare types of radio source such as Hybrid Morphology Radio Sources and one-sided jets, as well as a wide range of bent-tail and head-tail sources.

Figures (18)

• Figure 1: The process of manually scanning the image. The left-hand panel shows the area of the EMU-PS1 survey. The middle panel shows the raster pattern employed. The lines are separated by about 5 arcmin, and the raster box is about $10 \times 20$ arcmin, and is moved by about 10 arcmin in RA for each inspection, so that each point on the image is inspected at least 4 times. Thus, to cover the whole field requires about 500,000 manual inspections. As the whole field was scanned more than once, over a million inspections were performed in total.
• Figure 2: An example of a faint low-surface-brightness source that is not easily visible in the raw data but becomes obvious after spatial filtering, as described in Section 2.3. Left: raw unfiltered data. Right: filtered data. Although both lobes have some compact emission which is visible in the unfiltered EMU image, they appear as two disconnected compact sources and so were not included in our catalogue. Filtering reveals a radio galaxy with two connected low surface brightness lobes characteristic of aging electrons. Such sources that are visible only after spatial filtering are not included in our catalogue.
• Figure 3: Distributions of (a) the major axis size of the bounding box, and (b) total flux density of our DRAGNs. In both panels, the grey solid histograms show the distribution for the entire catalogue, while the coloured lines show the distributions for sources with some of the more common tags in our catalogue (see Section \ref{['sec:morphology']}).
• Figure 4: Classifying a source as FR1$_{\rm n}$ or FR2$_{\rm n}$ relies on the measurement of $a$ (the distance between the peaks) and $b$ (the total extent of the source). FR1$_{\rm n}$ have $a/b<0.5$ and FR2$_{\rm n}$ have $a/b > 0.5$. The top image satisfies the FR1$_{\rm n}$ criterion ($a/b < 0.5)$, and the centre image satisfies the FR2$_{\rm n}$ criterion ($a/b > 0.5)$. The bottom image satisfies the FR1$_{\rm n}$ criterion ($a/b < 0.5)$ but the small size combined with the measurement uncertainty makes the classification uncertain. We label such borderline cases as FRX$_{\rm n}$, as described in Section \ref{['sec:frx']}. All distances are in arcsec.
• Figure 5: Examples of HyMoRS$_{\rm n}$ sources, which appear to be FR1 on one side and FR2 on the other. In these and all subsequent multi-panel Figures, the white box is the rectangular region bounding box described in Section \ref{['extraction']} and the red cross is the tentative position of the host. If no cross is shown, then we were unable to identify a host.