A 600 kpc complex radio source at the center of Abell 3718 discovered by the EMU and POSSUM surveys
Bibliographic record
Abstract
Context. Multifrequency studies of galaxy clusters are crucial for inferring their dynamical states and physics. Moreover, these studies allow us to investigate cluster-embedded sources, whose evolution is affected by the physical and dynamical condition of the cluster itself. So far, these kinds of studies have been preferentially conducted on clusters visible from the northern hemisphere due to the high-fidelity imaging capabilities of ground-based radio interferometers located there. Aims. In this paper, we conducted a multifrequency study of the poorly known galaxy cluster Abell 3718. We investigated the unknown origin of an extended radio source with a length of ∼612 kpc at 943 MHz detected in images from the Evolutionary Map of the Universe (EMU) and POlarisation Sky Survey of the Universe’s Magnetism (POSSUM) surveys. Methods. We analyzed optical and X-ray data to infer the dynamical state of the cluster and, in particular, the merger activity. We conducted a radio spectral index study from 943 MHz up to 9 GHz. We also evaluated the polarization properties of the brightest cluster-embedded sources to understand if they are related to the radio emission observed on larger scales. Results. The cluster appears to be in a relaxed dynamical state, but there is clear asymmetry of the X-ray surface brightness distribution perpendicular to the direction of the largest angular extension of the radio source. The morphology of the cluster radio emission observed from 900 MHz to 9 GHz shows a system composed of a northern compact radio source and a southern radio galaxy whose jets are bent in the direction of an ultra-steep ( α ≈ 3.6), thin (few tens of kpc) arc of radio emission between the first two radio sources. The spectral index gradient along the radio source and the polarization images at high frequency suggest that the thin arc is an extension of the southern radio galaxy, which may have been energized by interacting with the X-ray gas. An additional structure extending to the northwest from the southern radio galaxy may be an unusual truncated radio jet that either failed to expand or faded away due to energy losses. Deeper X-ray and radio observations are needed to better constrain the physics at play in this cluster.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".