The impact of ionization morphology and X-ray heating on the cosmological 21-cm skew spectrum
Bibliographic record
Abstract
ABSTRACT The cosmological 21-cm signal offers a potential probe of the early Universe and the first ionizing sources. Current experiments probe the spatially dependent variance (Gaussianity) of the signal through the power spectrum (PS). The signal, however, is expected to be highly non-Gaussian due to the complex topology of reionization and X-ray heating. We investigate the non-Gaussianities of X-ray heating and reionization, by calculating the skew spectrum (SS) of the 21-cm signal using meraxes, which couples a semi-analytic galaxy population with seminumerical reionization simulations. The SS is the cross-spectrum of the quadratic temperature brightness field with itself. We generate a set of seven simulations from z = 30 to 5, varying the halo mass threshold for hosting star formation, the X-ray luminosity per star formation rate, and the minimum X-ray energy escaping host galaxies. We find the SS is predominantly negative as a function of redshift, transitioning to positive towards the start of reionization, and peaking during the mid-point of reionization. We do not see a negative dip in the SS during reionization, likely due to the specifics of modelling ionization sources. We normalize the SS by the PS during reionization isolating the non-Gaussianities. We find a trough ($k\sim \, 0.1\, \textrm {Mpc}^{-1}$) and peak ($k\sim \, 0.4{-}1\, \textrm {Mpc}^{-1}$) in the normalized SS during the mid-to-late periods of reionization. These correlate to the ionization topology, and neutral islands in the IGM. We calculate the cosmic variance of the normalized SS, and find these features are detectable in the absence of foregrounds with the SKA_LOW.
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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 | 0.003 |
| 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 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".