A Study of Nine High-Redshift Clusters of Galaxies. IV. Photometry and Spectra of Clusters 1324+3011 and 1604+4321
Bibliographic record
Abstract
New photometric and spectroscopic observations of galaxies in the directions of three distant clusters are presented as part of our ongoing high-redshift cluster survey. The clusters are Cl 1324+3011 at z = 0.76, Cl 1604+4304 at z = 0.90, and Cl 1604+4321 at z = 0.92. We have spectroscopically confirmed cluster membership for 20–40 galaxies in each system and have also obtained spectra for over 280 field galaxies spanning the range 0 < z < 2.5. Kinematic estimates of the mass within the central 770 h kpc of each cluster are in excess of 8 × 10 14 h M ⊙ . The observed X-ray luminosities in these clusters are at least a factor of 3 smaller than those observed in clusters with similar velocity dispersions at z ≤ 0.4. These clusters contain a significant population of elliptical-like galaxies, although these galaxies are not nearly as dominant as in massive clusters at z ≤ 0.5. We also find a large population of blue cluster members. Defining an active galaxy as one in which the rest equivalent width of [O II] is greater than 15 Å, the fraction of active cluster galaxies within the central 1.0 h Mpc is 45%. In the field population, we find that 65% of the galaxies with redshifts between z = 0.40 and z = 0.85 are active, while the fraction is 79% for field galaxies at z > 0.85. The star formation rate normalized by the rest-AB B -band magnitude, SFRN, increases as the redshift increases at a given evolving luminosity. At a given redshift, however, SFRN decreases linearly with increasing luminosity, indicating a remarkable insensitivity of the star formation rate to the intrinsic luminosity of the galaxy over the range -18 ≥ AB B ≥ -22. Cluster galaxies in the central 1 h Mpc regions exhibit depressed star formation rates and contain a larger fraction of galaxies with "k" -type spectra. The star formation rates in galaxies lying between 1 and 2.5 h Mpc from the cluster centers, however, are in good agreement with that in galaxies in the general field at similar redshifts. The spectroscopic and photometric properties of the cluster galaxies are well fitted by Bruzual & Charlot solar metallicity, constant-age (4.8 Gyr at z = 0.9), variable tau models. Metallicities in these clusters must be at least 0.2 of solar, and a significant amount of dust extinction is unlikely. We are able to measure significant evolution in the B -band luminosity function over the range 0.1 ≤ z ≤ 1. The characteristic luminosity increases by a factor of 3 with increasing redshift over this range. This result is consistent with an analysis of the luminosities of the brightest cluster galaxies (BCGs) in these clusters. The BCGs are typically twice as luminous as their current epoch counterparts.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 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) | 0.002 | 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".