COMAP Pathfinder – Season 2 results. III. Implications for cosmic molecular gas content at z ~ 3

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

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

Abstract

The Carbon monOxide Mapping Array Project (COMAP) Pathfinder survey continues to demonstrate the feasibility of line-intensity mapping using high-redshift carbon monoxide (CO) line emission traced at cosmological scales. The latest COMAP Pathfinder power spectrum analysis is based on observations through the end of Season 2, covering the first three years of Pathfinder operations. We use our latest constraints on the CO(1–0) line-intensity power spectrum atz~ 3 to update corresponding constraints on the cosmological clustering of CO line emission and thus the cosmic molecular gas content at a key epoch of galaxy assembly. We first mirror the COMAP Early Science interpretation, considering how Season 2 results translate to limits on the shot noise power of CO fluctuations and the bias of CO emission as a tracer of the underlying dark matter distribution. The COMAP Season 2 results place the most stringent limits on the CO tracer bias to date, at ⟨T b⟩ < 4.8 μK, which translates to a molecular gas density upper limit ofρH2< 1.6 × 108M⊙Mpc−3atz~ 3 given additional model assumptions. These limits narrow the model space significantly compared to previous CO line-intensity mapping results while maintaining consistency with small-volume interferometric surveys of resolved line candidates. The results also express a weak preference for CO emission models used to guide fiducial forecasts from COMAP Early Science, including our data-driven priors. We also consider directly constraining a model of the halo–CO connection, and show qualitative hints of capturing the total contribution of faint CO emitters through the improved sensitivity of COMAP data. With continued observations and matching improvements in analysis, the COMAP Pathfinder remains on track for a detection of cosmological clustering of CO emission.

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

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. The University of Toronto operates on the traditional land of the Huron-Wendat, the Seneca, and most recently, the Mississaugas of the Credit River; DTC is grateful to have the opportunity to work on this land. Research in Canada is supported by NSERC and CIFAR. 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. PCB acknowledges support from the James Arthur Postdoctoral Fellowship during the writing of this work. We acknowledge and thank the 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 agreements 772253 bits2cosmology and 819478 Cosmoglobe). HP acknowledges support from the Swiss National Science Foundation via Ambizione Grant PZ00P2_179934. This work was supported in part by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT, No. RS-2024-00340759). This study uses the Scientific color map acton (Crameri 2021) to prevent visual distortion of the data and exclusion of readers with color-vision deficiencies (Crameri et al. 2020). As in Chung et al. (2022) we thank Riccardo Pavesi for access to the COLDz ABC posterior sample used in this work. Many thanks also to George Stein for running and making available the original peak-patch simulations for use with the COMAP Pathfinder survey. This research made use of NASA’s Astrophysics Data System Bibliographic Services. Some of the methods for this work were originally tested on the Sherlock cluster; DTC would like to thank Stanford University and the Stanford Research Computing Center for providing computational resources and support that contributed to these research results. 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. Finally, we thank the anonymous referee for their constructive input towards the final state of this article.

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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