An Infrared Survey of Brightest Cluster Galaxies. II. Why are Some Brightest Cluster Galaxies Forming Stars?
Bibliographic record
Abstract
Quillen et al. presented an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray-luminous clusters. They found that at least half of these sources have signs of excess IR emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-IR emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star-forming galaxies. The gas depletion timescale is about 1 Gyr. The physical extent of the IR excess is consistent with that of the optical emission-line nebulae. This supports the hypothesis that star formation occurs in molecular gas associated with the emission-line nebulae and with evidence that the emission-line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates ( ) estimated from the X-ray emission and the star formation rates estimated from the IR luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates, suggesting that the reheating of the intracluster medium is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".