End-to-End Pipeline Methods for Full-Sky 21 cm Cosmology: Application to the CHIME Pathfinder Array
Bibliographic record
Abstract
The technique of 21 cm Line Intensity Mapping (LIM) has emerged as a promising new frontier in the field of observational cosmology, promising fast tomographic mapping of enormous volumes at the angular resolution needed to resolve Universe’s large-scale structure. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new cylindrical transit interferometer that has begun observations at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia. A two cylinder test-bed – the CHIME Pathfinder – has been surveying the Northern hemisphere in 1024 frequency bands between 400 and 800 MHz since the fall of 2015. These telescopes are optimized for 21 cm LIM at redshifts 0.8 − 2.5, targeting a time-resolved detection of the Baryon Acoustic Oscillations. Control of the systematics accompanied by modern interferometers has instituted a new philosophy of “end-to-end modelling” in the field: whereby the underlying signal, astrophysical foregrounds, telescope, and receiving electronics are modelled together in feedback with the data. In this thesis we describe the development of end-to-end analysis and forward modelling techniques for 21 cm LIM. First, we describe a novel subgrid biasing scheme for dark matter halo catalogs and its application to more accurate modelling of the intensity mapping signal component. The systematic focused on in this thesis is the angular response function, or “beam,” of the interferometer. We go on to describe the radio holography technique implemented to measure this function for each of the CHIME Pathfinder’s 256 inputs and develop a data analysis pipeline capable of converting time-ordered data to a beam model for input to the mapmaker. Finally, we present a modification of the m-mode formalism mapmaker, designed explicitly for full-sky 21 cm LIM, which relaxes the usual assumption of statistical isotropy of the signal, allowing it to treat arbitrarily realistic sky models. We then exploit these tools to deconvolve CHIME Pathfinder maps with the beam model constructed from holography, and find a minimum factor of 2 improvement over previous methods. In its entirety, this thesis forms a foundation for the methods necessary extract accurate cosmological information from modern interferometers such as CHIME and its Pathfinder.
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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 | 0.000 | 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 | 0.000 |
| 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 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".