THE GROWTH OF COOL CORES AND EVOLUTION OF COOLING PROPERTIES IN A SAMPLE OF 83 GALAXY CLUSTERS AT 0.3 <<i>z</i>< 1.2 SELECTED FROM THE SPT-SZ SURVEY
Bibliographic record
Abstract
We present first results on the cooling properties derived from Chandra X-ray observations of 83 high-redshift (0.3 < z < 1.2) massive galaxy clusters selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope data.We measure each cluster's central cooling time, central entropy, and mass deposition rate, and compare these properties to those for local cluster samples.We find no significant evolution from z ∼ 0 to z ∼ 1 in the distribution of these properties, suggesting that cooling in cluster cores is stable over long periods of time.We also find that the average cool core entropy profile in the inner ∼100 kpc has not changed dramatically since z ∼ 1, implying that feedback must be providing nearly constant energy injection to maintain the observed "entropy floor" at ∼10 keV cm 2 .While the cooling properties appear roughly constant over long periods of time, we observe strong evolution in the gas density profile, with the normalized central density (ρ g,0 /ρ crit ) increasing by an order of magnitude from z ∼ 1 to z ∼ 0. When using metrics defined by the inner surface brightness profile of clusters, we find an apparent lack of classical, cuspy, cool-core clusters at z > 0.75, consistent with earlier reports for clusters at z > 0.5 using similar definitions.Our measurements indicate that cool cores have been steadily growing over the 8 Gyr spanned by our sample, consistent with a constant, ∼150 M yr -1 cooling flow that is unable to cool below entropies of 10 keV cm 2 and, instead, accumulates in the cluster center.We estimate that cool cores began to The Astrophysical Journal, 774:23 (23pp), 2013 September 1 McDonald et al.assemble in these massive systems at z cool = 1.0 +1.0 -0.2 , which represents the first constraints on the onset of cooling in galaxy cluster cores.At high redshift (z 0.75), galaxy clusters may be classified as "cooling flows" (low central entropy, cooling time) but not "cool cores" (cuspy surface brightness profile), meaning that care must be taken when classifying these high-z systems.We investigate several potential biases that could conspire to mimic this cool core evolution and are unable to find a bias that has a similar redshift dependence and a substantial amplitude.
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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 | 0.001 |
| 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".