COMAP Pathfinder – Season 2 results. I. Improved data selection and processing

Creators: Lunde, J. G. S.¹; Stutzer, N.-O.¹; Breysse, P. C.^{2, 3}; Chung, D. T.^{4, 5, 6}; Cleary, K. A.⁷; Dunne, D. A.⁷; Eriksen, H. K.¹; Harper, S. E.⁸; Ihle, H. T.¹; Lamb, J. W.⁷; Pearson, T. J.⁷; Philip, L.^{9, 10}; Wehus, I. K.¹; Woody, D. P.⁷; Bond, J. R.^{4, 5}; Church, S. E.¹¹; Gaier, T.⁹; Gundersen, J. O.¹²; Harris, A. I.¹³; Hobbs, R.⁷; Kim, J.¹⁴; Lawrence, C. R.⁹; Murray, N.^{4, 5}; Padmanabhan, H.¹⁵; Readhead, Anthony C. S.⁷; Rennie, T. J.^{8, 16}; Tolgay, D.^{4, 5}; COMAP Collaboration

1. University of Oslo
2. New York University
3. Southern Methodist University
4. Canadian Institute for Theoretical Astrophysics
5. University of Toronto
6. Cornell University
7. California Institute of Technology
8. University of Manchester
9. Jet Propulsion Lab
10. Brookhaven National Laboratory
11. Stanford University
12. University of Miami
13. University of Maryland, College Park
14. Korea Advanced Institute of Science and Technology
15. University of Geneva
16. University of British Columbia

Abstract

The CO Mapping Array Project (COMAP) Pathfinder is performing line intensity mapping of CO emission to trace the distribution of unresolved galaxies at redshiftz ∼ 3. We present an improved version of the COMAP data processing pipeline and apply it to the first two Seasons of observations. This analysis improves on the COMAP Early Science (ES) results in several key aspects. On the observational side, all second season scans were made in constant-elevation mode, after noting that the previous Lissajous scans were associated with increased systematic errors; those scans accounted for 50% of the total Season 1 data volume. In addition, all new observations were restricted to an elevation range of 35–65 degrees to minimize sidelobe ground pickup. On the data processing side, more effective data cleaning in both the time and map domain allowed us to eliminate all data-driven power spectrum-based cuts. This increases the overall data retention and reduces the risk of signal subtraction bias. However, due to the increased sensitivity, two new pointing-correlated systematic errors have emerged, and we introduced a new map-domain PCA filter to suppress these errors. Subtracting only five out of 256 PCA modes, we find that the standard deviation of the cleaned maps decreases by 67% on large angular scales, and after applying this filter, the maps appear consistent with instrumental noise. Combining all of these improvements, we find that each hour of raw Season 2 observations yields on average 3.2 times more cleaned data compared to the ES analysis. Combining this with the increase in raw observational hours, the effective amount of data available for high-level analysis is a factor of eight higher than in the ES analysis. The resulting maps have reached an uncertainty of 25–50 μK per voxel, providing by far the strongest constraints on cosmological CO line emission published to date.

Copyright and License

© The Authors 2024. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

We acknowledge support from the Research Council of Norway through grants 251328 and 274990, and from the European Research Council (ERC) under the Horizon 2020 Research and Innovation Program (Grant agreement No. 772253 bits2cosmology and 819478 Cosmoglobe) This material is based upon work supported by the National Science Foundation under Grant Nos. 1517108, 1517288, 1517598, 1518282, 1910999, and 2206834, as well as by the Keck Institute for Space Studies under “The First Billion Years: A Technical Development Program for Spectral Line Observations”. Parts of the work were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. HP acknowledges support from the Swiss National Science Foundation via Ambizione Grant PZ00P2_179934. SEH and CD acknowledge funding from an STFC Consolidated Grant (ST/P000649/1) and a UKSA grant (ST/Y005945/1) funding LiteBIRD foreground activities. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (RS-2024-00340759). PCB was supported by the James Arthur Postdoctoral Fellowship. DTC was supported by a CITA/Dunlap Institute postdoctoral fellowship for much of this work. The Dunlap Institute is funded through an endowment established by the David Dunlap family and the University of Toronto. Research in Canada is supported by NSERC and CIFAR. JGSL and NOS thank Sigurd K. Næss for all the fruitful discussions in the office, and while biking through nature, during the last three years. This work was first presented at the Line Intensity Mapping 2024 conference held in Urbana, Illinois; we thank Joaquin Vieira and the other organizers for their hospitality and the participants for useful discussions. JGSL and NOS thanks the 2023 Stockholm Beam Mode workshop for discussions on beam convolution.

Software References

Software acknowledgments. Matplotlib for plotting (Hunter 2007); NumPy (Harris et al. 2020) and SciPy (Virtanen et al. 2020) for efficient numerics and array handling in Python; Astropy a community made core Python package for astronomy (Astropy Collaboration 2013, 2018, 2022); Multi-node parallelization with MPI for Python (Dalcín et al. 2005, 2008; Dalcin et al. 2011; Dalcin & Fang 2021); Pixell (https://github.com/simonsobs/pixell) for handling sky maps in rectangular pixelization.

Additional Information

Published together:

COMAP Pathfinder – Season 2 results. I. Improved data selection and processing. https://doi.org/10.1051/0004-6361/202451121
COMAP Pathfinder – Season 2 results. II. Updated constraints on the CO(1–0) power spectrum. https://doi.org/10.1051/0004-6361/202451123
COMAP Pathfinder – Season 2 results. III. Implications for cosmic molecular gas content at z ~ 3. https://doi.org/10.1051/0004-6361/202451122.

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