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

   https://doi.org/10.3847/1538-4357/ac63c7  

   Chung, Dongwoo T.; Breysse, Patrick C.; Cleary, Kieran A.; Ihle, Håvard T.; Padmanabhan, Hamsa; Silva, Marta B.; Richard Bond, J.; Borowska, Jowita; Catha, Morgan; Church, Sarah E.; et al (July 2022, The Astrophysical Journal)

   Abstract We present the current state of models for the z ∼ 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 clust ≲ 70 μ K 2 greatly improves on the indirect upper limit of 420 μ K 2 reported from the CO Power Spectrum Survey (COPSS) measurement at k ∼ 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 ≲ 50 μ K 2 , and the cosmic molecular gas density, ρ H2 < 2.5 × 10 8 M ⊙ 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. 

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2. COMAP Pathfinder – Season 2 results: II. Updated constraints on the CO(1–0) power spectrum

   https://doi.org/10.1051/0004-6361/202451123  

   Stutzer, N-O; Lunde, J_G S; Breysse, P C; Chung, D T; Cleary, K A; Dunne, D A; Eriksen, H K; Ihle, H T; Padmanabhan, H; Tolgay, D; et al (November 2024, Astronomy & Astrophysics)

   We present updated constraints on the cosmological 3D power spectrum of carbon monoxide CO(1–0) emission in the redshift range 2.4–3.4. The constraints are derived from the two first seasons of Carbon monOxide Mapping Array Project (COMAP) Pathfinder line intensity mapping observations aiming to trace star formation during the epoch of galaxy assembly. These results improve on the previous Early Science results through both increased data volume and an improved data processing methodology. On the methodological side, we now perform cross-correlations between groups of detectors (“feed groups”), as opposed to cross-correlations between single feeds, and this new feed group pseudo power spectrum (FGPXS) is constructed to be more robust against systematic effects. In terms of data volume, the effective mapping speed is significantly increased due to an improved observational strategy as well as a better data selection methodology. The updated spherically and field-averaged FGPXS,C^~(k), is consistent with zero, at a probability-to-exceed of around 34%, with an excess of 2.7σin the most sensitive bin. Our power spectrum estimate is about an order of magnitude more sensitive in our six deepest bins across 0.09 Mpc⁻¹<k< 0.73 Mpc⁻¹, compared to the feed-feed pseudo power spectrum (FPXS) of COMAP ES. Each of these bins individually constrains the CO power spectrum tok P_CO(k) < 2400–4900 μK²Mpc²at 95% confidence. To monitor potential contamination from residual systematic effects, we analyzed a set of 312 difference-map null tests and found that these are consistent with the instrumental noise prediction. In sum, these results provide the strongest direct constraints on the cosmological 3D CO(1–0) power spectrum published to date. 

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3. COMAP Early Science. I. Overview

   https://doi.org/10.3847/1538-4357/ac63cc  

   Cleary, Kieran A.; Borowska, Jowita; Breysse, Patrick C.; Catha, Morgan; Chung, Dongwoo T.; Church, Sarah E.; Dickinson, Clive; Eriksen, Hans Kristian; Foss, Marie Kristine; Gundersen, Joshua Ott; et al (July 2022, The Astrophysical Journal)

   Abstract The CO Mapping Array Project (COMAP) aims to use line-intensity mapping of carbon monoxide (CO) to trace the distribution and global properties of galaxies over cosmic time, back to the Epoch of Reionization (EoR). To validate the technologies and techniques needed for this goal, a Pathfinder instrument has been constructed and fielded. Sensitive to CO(1–0) emission from z = 2.4–3.4 and a fainter contribution from CO(2–1) at z = 6–8, the Pathfinder is surveying 12 deg 2 in a 5 yr observing campaign to detect the CO signal from z ∼ 3. Using data from the first 13 months of observing, we estimate P CO ( k ) = −2.7 ± 1.7 × 10 4 μ K 2 Mpc 3 on scales k = 0.051 −0.62 Mpc −1 , the first direct three-dimensional constraint on the clustering component of the CO(1–0) power spectrum. Based on these observations alone, we obtain a constraint on the amplitude of the clustering component (the squared mean CO line temperature bias product) of Tb 2 < 49 μ K 2 , nearly an order-of-magnitude improvement on the previous best measurement. These constraints allow us to rule out two models from the literature. We forecast a detection of the power spectrum after 5 yr with signal-to-noise ratio (S/N) 9–17. Cross-correlation with an overlapping galaxy survey will yield a detection of the CO–galaxy power spectrum with S/N of 19. We are also conducting a 30 GHz survey of the Galactic plane and present a preliminary map. Looking to the future of COMAP, we examine the prospects for future phases of the experiment to detect and characterize the CO signal from the EoR. 

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

   https://doi.org/10.1051/0004-6361/202451121  

   Lunde, J_G S; Stutzer, N-O; Breysse, P C; Chung, D T; Cleary, K A; Dunne, D A; Eriksen, H K; Harper, S E; Ihle, H T; Lamb, J W; et al (November 2024, Astronomy & Astrophysics)

   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. 

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5. COMAP Early Science. VII. Prospects for CO Intensity Mapping at Reionization

   https://doi.org/10.3847/1538-4357/ac63c9  

   Breysse, Patrick C.; Chung, Dongwoo T.; Cleary, Kieran A.; Ihle, Håvard T.; Padmanabhan, Hamsa; Silva, Marta B.; Bond, J. Richard; Borowska, Jowita; Catha, Morgan; Church, Sarah E.; et al (July 2022, The Astrophysical Journal)

   Abstract We introduce COMAP-EoR, the next generation of the Carbon Monoxide Mapping Array Project aimed at extending CO intensity mapping to the Epoch of Reionization. COMAP-EoRsupplements the existing 30 GHz COMAP Pathfinder with two additional 30 GHz instruments and a new 16 GHz receiver. This combination of frequencies will be able to simultaneously map CO(1–0) and CO(2–1) at reionization redshifts (z∼ 5–8) in addition to providing a significant boost to thez∼ 3 sensitivity of the Pathfinder. We examine a set of existing models of the EoR CO signal, and find power spectra spanning several orders of magnitude, highlighting our extreme ignorance about this period of cosmic history and the value of the COMAP-EoRmeasurement. We carry out the most detailed forecast to date of an intensity mapping cross correlation, and find that five out of the six models we consider yield signal to noise ratios (S/Ns) ≳ 20 for COMAP-EoR, with the brightest reaching a S/N above 400. We show that, for these models, COMAP-EoRcan make a detailed measurement of the cosmic molecular gas history fromz∼ 2–8, as well as probe the population of faint, star-forming galaxies predicted by these models to be undetectable by traditional surveys. We show that, for the single model that does not predict numerous faint emitters, a COMAP-EoR-type measurement is required to rule out their existence. We briefly explore prospects for a third-generation Expanded Reionization Array (COMAP-ERA) capable of detecting the faintest models and characterizing the brightest signals in extreme detail. 

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