COMAP Early Science. V. Constraints and Forecasts at z ∼ 3

We present the current state of models for the z similar to 3 carbon monoxide (CO) line intensity signal targeted by the CO Mapping Array Project (COMAP) Pathfinder in the context of its early science results. Our fiducial model, relating dark matter halo properties to CO luminosities, informs parameter priors with empirical models of the galaxy-halo connection and previous CO (1-0) observations. The Pathfinder early science data spanning wavenumbers k = 0.051-0.62 Mpc(-1) represent the first direct 3D constraint on the clustering component of the CO (1-0) power spectrum. Our 95% upper limit on the redshift-space clustering amplitude A(chist) less than or similar to 70 mu K-2 greatly improves on the indirect upper limit of 420 mu K-2 reported from the CO Power Spectrum Survey (COPSS) measurement at k similar to 1 Mpc(-1). The COMAP limit excludes a subset of models from previous literature and constrains interpretation of the COPSS results, demonstrating the complementary nature of COMAP and interferometric CO surveys. Using line bias expectations from our priors, we also constrain the squared mean line intensity bias product,( )< Tb >(2)( )less than or similar to 50 mu K-2, and the cosmic molecular gas density, rho(H2) < 2.5 x 10(8) M-circle dot, Mpc(-3) (95% upper limits). Based on early instrument performance and our current CO signal estimates, we forecast that the 5 yr Pathfinder campaign will detect the CO power spectrum with overall signal-to-noise ratio of 9-17. Between then and now, we also expect to detect the CO-galaxy cross-spectrum using overlapping galaxy survey data, enabling enhanced inferences of cosmic star formation and galaxy evolution history.