Cosmological parameters from the comparison of peculiar velocities with predictions from the 2M++ density field
Bibliographic record
Abstract
Peculiar velocity measurements are the only tool available in the low-redshift Universe for mapping the large-scale distribution of matter and can thus be used to constrain cosmology. Using redshifts from the 2M++ redshift compilation, we reconstruct the density of galaxies within 200 h−1 Mpc, allowing for the first time good sampling of important superclusters such as the Shapley Concentration. We compare the predicted peculiar velocities from 2M++ to Tully–Fisher and SNe peculiar velocities. We find a value of β* |$\equiv \Omega _{\rm {m}}^{0.55}/b^* =$| 0.431 ± 0.021, suggesting |$\Omega _{\rm {m}}^{0.55}\sigma _{\rm {8,lin}}$| = 0.401 ± 0.024, in good agreement with other probes. The predicted peculiar velocity of the Local Group arising from the 2M++ volume alone is 540 ± 40 km s−1, towards l = 268° ± 4°, b = 38° ± 6°, only 10° out of alignment with the cosmic microwave background dipole. To account for velocity contributions arising from sources outside the 2M++ volume, we fit simultaneously for β* and an external bulk flow in our analysis. We find that an external bulk flow is preferred at the 5.1σ level, and the best fit has a velocity of 159 ± 23 km s− 1 towards l = 304° ± 11°, b = 6° ± 13°. Finally, the predicted bulk flow of a 50 h−1 Mpc Gaussian-weighted volume centred on the Local Group is 230 ± 30 km s−1, in the direction l = 293° ± 8°, b = 14° ± 10°, in agreement with predictions from Λ cold dark matter.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 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 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".