Abell 1758N from an optical point of view: new insights on a merging cluster with diffuse radio emission
Bibliographic record
Abstract
Context. The mechanisms producing the diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated. Aims. We seek to explore the internal dynamics of the cluster Abell 1758N, which has been shown to host a radio halo and two relics, and is known to be a merging bimodal cluster. Methods. Our analysis is mainly based on new redshift data for 137 galaxies acquired at the Telescopio Nazionale Galileo, only four of which have redshifts previously listed in the literature. We also used photometric data from the Sloan Digital Sky Survey and from the Canada-France-Hawaii Telescope archive. We combined galaxy velocities and positions to select 92 cluster galaxies and analyzed the internal cluster dynamics. Results. We estimate a cluster redshift of ⟨z⟩ = 0.2782 and quite a high line-of-sight (LOS) velocity dispersion σV ~ 1300 km s-1. Our 2D analysis confirms the presence of a bimodal structure along the NW–SE direction. We add several pieces of information to the previous merging scenario: the two subclusters (here A1758N(NW) and A1758N(SE)) cannot be separated in the velocity analyses and we deduce a small LOS velocity difference (ΔVrf,LOS ≲ 300 km s-1 in the cluster rest-frame). The velocity information successfully shows that A1758N is surrounded by two small groups and active galaxies infalling onto, or escaping from, the cluster. Removing the two groups, we estimate σV,NW ~ 1000 km s-1 and σV,SE ~ 800 km s-1 for A1758N(NW) and A1758N(SE), respectively. We find that Abell 1758N is a very massive cluster with a range of M = 2−3 × 1015 h70-1 M⊙, depending on the adopted model. Conclusions. As expected for clusters that host powerful, extended, diffuse radio emissions, Abell 1758N is a major cluster merger just forming a massive system.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".