<i>Euclid</i> : Star clusters in IC 342, NGC 2403, and Holmberg II
Bibliographic record
Abstract
We examine the star cluster populations in the three nearby (3.20–3.45 Mpc) galaxies IC 342, NGC 2403, and Holmberg II, observed as part of the Euclid Early Release Observations programme. Our main focus in this paper is old globular clusters (GCs), for which the wide field of view and excellent image quality of Euclid offer substantial advantages over previous works. With respect to IC 342, in particular, this is the first study of stellar clusters that goes beyond its nuclear cluster. After a selection process based on size and magnitude criteria, followed by visual inspection, we identified 111 old (≳1 Gyr) GC candidates in IC 342, 49 in NGC 2403 (of which 15 were previously known), along with 7 in Holmberg II. In addition, a number of younger and/or intermediate-age candidates were identified. The colour distributions of GC candidates in the two larger galaxies show hints of bimodality, with peaks at ( I E −{H E ) 0 = 0.36 and 0.79 in both IC 342 and NGC 2403, corresponding to metallicities of [Fe/H] ≈ −1.5 and [Fe/H] ≈ −0.5. These results are similar to those reported for the metal-poor and metal-rich GC subpopulations in the Milky Way. The luminosity functions of our GC candidates exhibit an excess of relatively faint objects, relative to a canonical, approximately Gaussian GC luminosity function (GCLF). Although some contamination from background galaxies and younger clusters might be present in our GC samples, we argue that the excess could be at least partially real. In particular, we find this could be the case for IC 342, where the excess objects could be similar to those previously identified, for example, in M101 and NGC 6946. The specific frequency of old GCs in IC 342, as determined on the basis of the brighter half of the GCLF, appears to be unusually low with S N ≈ 0.2–0.3. The combined luminosity function of young and intermediate-age clusters in all three galaxies is consistent with a power-law distribution of d N /d L ∝ L −2.3 ± 0.1 . The total numbers of young clusters brighter than M ( I E ) = −8 in NGC 2403 and Holmberg II are comparable with those found in their Local Group counterparts, namely, M33 and the Small Magellanic Cloud, respectively.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".