Spectroscopic Constraints on the Buildup of Intracluster Light in the Coma Cluster
Bibliographic record
Abstract
Abstract The stellar content of the intracluster light (ICL) provides unique insight into the hierarchical assembly process of galaxy clusters. We present optical spectra of three ICL regions ( μ g ≈ 25.3–26.2 mag arcsec −2 ) in the Coma cluster, located between 100 and 180 kpc from their nearest brightest cluster galaxies (BCGs): NGC 4889 and NGC 4874. Integral-field unit (IFU) spectroscopy with 13.5 hr on-source integration was acquired in an ancillary program within the Sloan Digital Sky Survey-IV MaNGA survey. We stacked the 127 individual fiber spectra in each IFU to achieve a 1 σ limiting surface brightness of 27.9 mag arcsec −2 , corresponding to a mean signal-to-noise ratio in the optical of 21.7, 9.0, and 11.7 Å −1 , for each ICL region. We apply stellar population models to the stacked spectra. Our results show that the velocity dispersions of ICL regions are very high ( σ ∼ 630 km s −1 ), indicating the stars in these regions are tracing the gravitational potential of the cluster, instead of any individual galaxy. The line-of-sight velocities are different from each other by ∼700 km s −1 , while the velocity of each region is similar to the closest BCG. This suggests that the ICL regions are associated with two distinct subclusters centered on NGC 4889 and NGC 4874. The stellar populations of these regions are old and metal-poor, with ages of , , and Gyr, and [Fe/H] of , , and . From the derived age and metallicity, the buildup of ICL in Coma is likely to be through the accretion of low-mass galaxies or the tidal stripping of the outskirts of massive galaxies that have ended their star formation early on, instead of directly from major mergers of massive galaxies.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 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".