The properties and evolution of a K-band selected sample of massive galaxies at z∼ 0.4-2 in the Palomar/DEEP2 survey
Bibliographic record
Abstract
We present the results of a study on the properties and evolution of massive (M* > 1011 M⊙) galaxies at z∼ 0.4–2 utilizing Keck spectroscopy, near‐infrared Palomar imaging, and Hubble, Chandra and Spitzer data covering fields targeted by the DEEP2 galaxy spectroscopic survey. Our sample is K‐band selected and stellar mass limited, based on wide‐area near‐infrared imaging from the Palomar Observatory Wide‐Field Infrared Survey, which covers 1.53 deg2 to a 5σ depth of Ks,vega∼ 20.5. Our primary goal is to obtain a broad census of massive galaxies through measuring how their number and mass densities, morphology, as well as their star formation and active galactic nucleus content evolve from z∼ 0.4–2. Our major findings include: (i) statistically the mass and number densities of M* > 1011 M⊙ galaxies show little evolution between z= 0 and 1 and from z∼ 0 to 2 for M* > 1011.5 M⊙ galaxies. We however find significant evolution within 1 < z < 1.5 for 1011 M⊙ < M* < 1011.5 M⊙ galaxies. (ii) After examining the structures of our galaxies using Hubble ACS imaging, we find that M* > 1011 M⊙ selected galaxies show a nearly constant elliptical fraction of ∼70–90 per cent at all redshifts. The remaining objects tend to be peculiars possibly undergoing mergers at z > 0.8, while spirals dominate the remainder at lower redshifts. A significant fraction (∼25 per cent) of these early‐types contain minor structural anomalies. (iii) We find that only a fraction (∼60 per cent) of massive galaxies with M* > 1011 M⊙ are on the red sequence at z∼ 1.4, while nearly 100 per cent evolve on to it by z∼ 0.4. (iv) By utilizing Spitzer MIPS imaging and [O ii] line fluxes we argue that M* > 1011.5 M⊙ galaxies have a steeply declining star formation rate (SFR) density ∼ (1 +z)6. By examining the contribution of star formation to the evolution of the mass function, as well as the merger history through the CAS parameters, we determine that M* > 1011 M⊙ galaxies undergo on average 0.9+0.7−0.5 major mergers at 0.4 < z < 1.4. (v) We find that a high (5 per cent) fraction of all M* > 1011 M⊙ galaxies are X‐ray emitters. Roughly half of these are morphologically distorted ellipticals or peculiars. Finally, we compare our mass growth with semi‐analytical models from the Millennium Simulation, finding relative good agreement at z < 2 for the M* < 1011.5 M⊙ systems, but that the number and mass densities of M* > 1011.5 M⊙ galaxies are underpredicted by a factor of >100.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".