COMAP Pathfinder – Season 2 results

III. Implications for cosmic molecular gas content at z ~ 3

¹ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
² Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
³ Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
⁴ Center for Cosmology and Particle Physics, Department of Physics, New York University, 726 Broadway, New York, NY 10003, USA
⁵ Department of Physics, Southern Methodist University, Dallas, TX 75275, USA
⁶ California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁷ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
⁸ Departement de Physique Théorique, Universite de Genève, 24 Quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
⁹ Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON M5S 1A7, Canada
¹⁰ David A. Dunlap Department of Astronomy, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4, Canada
¹¹ Kavli Institute for Particle Astrophysics and Cosmology & Physics Department, Stanford University, Stanford, CA 94305, USA
¹² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹³ Department of Physics, University of Miami, 1320 Campo Sano Avenue, Coral Gables, FL 33146, USA
¹⁴ Jodrell Bank Centre for Astrophysics, Department of Physics & Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹⁵ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹⁶ Owens Valley Radio Observatory, California Institute of Technology, Big Pine, CA 93513, USA
¹⁷ Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
¹⁸ Brookhaven National Laboratory, Upton, NY 11973-5000, USA
¹⁹ Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada

^★ Corresponding author; dongwooc@cornell.edu

Received: 14 June 2024
Accepted: 23 September 2024

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 at z ~ 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 of ρ_H2 < 1.6 × 10⁸ M_⊙ Mpc⁻³ at z ~ 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.