Cosmological parameters from the comparison of peculiar velocities with predictions from the 2M++ density field
Why this work is in the frame
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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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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 | 0.000 | 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 | 0.001 | 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 it