Jonas Gahr Sturtzel Lunde

• Dunne, D. A.; Cleary, K. A.; Breysse, P. C.; Chung, D. T.; Ihle, Håvard Tveit & Lunde, Jonas Gahr Sturtzel [Show all 12 contributors for this article] (2025). Three-dimensional stacking as a line intensity mapping statistic. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 702. doi: 10.1051/0004-6361/202554780. Full text in Research Archive Show summary

  Line intensity mapping (LIM) is a growing technique that measures the integrated spectral line emission from unresolved galaxies over a three-dimensional region of the Universe. Although LIM experiments ultimately aim to provide powerful cosmological constraints via auto-correlation, many LIM experiments are also designed to take advantage of overlapping galaxy surveys, thus enabling joint analyses of two datasets. We introduce a flexible simulation pipeline that can generate mock galaxy surveys and mock LIM data simultaneously for the same population of simulated galaxies. Using this pipeline, we explore a simple joint analysis technique: three-dimensional co-addition (stacking) of LIM data on the positions of galaxies from a traditional galaxy catalogue. We test how the output of this technique reacts to changes in experimental design of both the LIM experiment and the galaxy survey, its sensitivity to various astrophysical parameters, and its susceptibility to common systematic errors. We find that an ideal catalogue for a stacking analysis targets as many high-mass dark matter halos as possible. We also find that the signal in a LIM stacking analysis originates almost entirely from the large-scale clustering of halos around the catalogue objects rather than the catalogue objects themselves. While stacking is a sensitive and conceptually simple way to achieve a LIM detection, thus providing a valuable way to validate a LIM auto-correlation detection, it will likely require a full cross-correlation to achieve further characterisation of the galaxy tracers involved, as the cosmological and astrophysical parameters we explore here have degenerate effects on the stack.

• Stutzer, Nils-Ole; Lunde, Jonas Gahr Sturtzel; Breysse, P.C.; Chung, D.T.; Cleary, K.A. & Dunne, D.A. [Show all 27 contributors for this article] (2024). COMAP Pathfinder – Season 2 results: II. Updated constraints on the CO(1–0) power spectrum. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 691. doi: 10.1051/0004-6361/202451123. Full text in Research Archive Show summary

  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 2.7 σ in 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 to k PCO(k) < 2400–4900 μK2Mpc2 at 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.

• Harper, Stuart E.; Dickinson, Clive; Cleary, Kieran A.; Hensley, Brandon S.; Hoerning, Gabriel A. & Paladini, Roberta [Show all 18 contributors for this article] (2024). COMAP Galactic science I: observations of spinning dust emission at 30 GHz in dark clouds surrounding the λ-Orionis H II region. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 536(3), p. 2914–2935. doi: 10.1093/mnras/stae2749. Full text in Research Archive
• Chung, D.T.; Breysse, P.C.; Cleary, K.A.; Dunne, D.A.; Lunde, Jonas Gahr Sturtzel & Padmanabhan, H. [Show all 27 contributors for this article] (2024). COMAP Pathfinder – Season 2 results: III. Implications for cosmic molecular gas content at z ∼ 3. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 691. doi: 10.1051/0004-6361/202451122. Full text in Research Archive Show summary

  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 ρH2 < 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.

• Lunde, Jonas Gahr Sturtzel; Stutzer, Nils-Ole; Breysse, P.C.; Chung, D.T.; Cleary, K.A. & Dunne, D.A. [Show all 27 contributors for this article] (2024). COMAP Pathfinder – Season 2 results: I. Improved data selection and processing. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 691. doi: 10.1051/0004-6361/202451121. Full text in Research Archive Show summary

  The CO Mapping Array Project (COMAP) Pathfinder is performing line intensity mapping of CO emission to trace the distribution of unresolved galaxies at redshift z ∼ 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.

• Dunne, Delaney A.; Cleary, Kieran A.; Breysse, Patrick C.; Chung, Dongwoo T.; Ihle, Håvard Tveit & Bond, J. Richard [Show all 25 contributors for this article] (2024). COMAP Early Science. VIII. A Joint Stacking Analysis with eBOSS Quasars. The Astrophysical Journal (ApJ). ISSN 0004-637X. 965(1). doi: 10.3847/1538-4357/ad2dfc. Full text in Research Archive
• Watts, Duncan; Fuskeland, Unni; Aurvik, Ragnhild; Basyrov, Artem; Bianchi, L.A. & Brilenkov, Maksym [Show all 21 contributors for this article] (2024). COSMOGLOBE DR1 results: III. First full-sky model of polarized synchrotron emission from all WMAP and Planck LFI data. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 686. doi: 10.1051/0004-6361/202348330. Full text in Research Archive Show summary

  We present the first model of full-sky polarized synchrotron emission that is derived from all WMAP and Planck LFI frequency maps. The basis of this analysis is the set of end-to-end reprocessed COSMOGLOBE Data Release 1 (DR1) sky maps presented in a companion paper, which have significantly lower instrumental systematics than the legacy products from each experiment. We find that the resulting polarized synchrotron amplitude map has an average noise rms per 2° full width at half maximum (FWHM) beam of 3.2 μK at 30 GHz. This is 30% lower than the recently released BEYONDPLANCK model that included only LFI+WMAP Ka–V data, and 29% lower than the WMAP K-band map alone. The mean B-to-E power spectrum ratio is 0.39 ± 0.02, with amplitudes consistent with those measured previously by Planck and QUIJOTE. Assuming a power law model for the synchrotron spectral energy distribution and using the T–T plot method, we find a full-sky inverse noise-variance-weighted mean of the synchrotron polarized spectral index of βs = −3.07 ± 0.07 from the COSMOGLOBE DR1 K band and 30 GHz, in good agreement with previous estimates. In summary, the novel COSMOGLOBE DR1 synchrotron model is both more sensitive and systematically cleaner than similar previous models, and it has a more complete error description that is defined by a set of Monte Carlo posterior samples. We believe that these products are preferable over previous Planck and WMAP products for all synchrotron-related scientific applications, including simulations, forecasting, and component separation.

• Basyrov, Artem; Stutzer, Nils-Ole; Lunde, Jonas Gahr Sturtzel; Eriksen, Hans Kristian Kamfjord; Gjerløw, Eirik & Watts, Duncan [Show all 7 contributors for this article] (2024). Optimal bolometer transfer function deconvolution for CMB experiments through maximum likelihood mapmaking. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 688. doi: 10.1051/0004-6361/202450712. Full text in Research Archive Show summary

  We revisit the impact of finite time responses of bolometric detectors used for deep observations of the cosmic microwave background (CMB). Until now, bolometer transfer functions have been accounted for through a two-step procedure by first deconvolving an estimate of their Fourier-space representation from the raw time-ordered data (TOD), and then averaging the deconvolved TOD into pixelized maps. However, for many experiments, including the Planck High Frequency Instrument (HFI), it is necessary to apply an additional low-pass filter to avoid an excessive noise boost, which leads to an asymmetric effective beam. In this paper we demonstrate that this effect can be avoided if the transfer function deconvolution and pixelization operations are performed simultaneously through integrated maximum likelihood mapmaking. The resulting algorithm is structurally identical to the artDeco algorithm for beam deconvolution. We illustrate the relevance of this method with simulated Planck HFI 143 GHz data, and find that the resulting effective beam is both more symmetric than with the two-step procedure, resulting in a sky-averaged ellipticity that is 64% lower, and an effective beam full-width-at-half-maximum (FWHM) that is 2.3% smaller. Similar improvements are expected for any other bolometer-based CMB experiments with long time constants.

• Eskilt, Johannes Røsok; Watts, Duncan; Aurvik, Ragnhild; Basyrov, Artem; Bersanelli, Marco & Brilenkov, Maksym [Show all 31 contributors for this article] (2023). Cosmoglobe DR1 results II. Constraints on isotropic cosmic birefringence from reprocessed WMAP and Planck LFI data. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 679. doi: 10.1051/0004-6361/202346829. Full text in Research Archive Show summary

  Cosmic birefringence is a parity-violating effect that might have rotated the plane of the linearly polarized light of the cosmic microwave background (CMB) by an angle β since its emission. This angle has recently been measured to be nonzero at a statistical significance of 3.6 σ in the official Planck PR4 and 9-year WMAP data. In this work, we constrain β using the reprocessed B EYOND P LANCK LFI and C OSMOGLOBE DR1 WMAP polarization maps. These novel maps have both lower systematic residuals and a more complete error description than the corresponding official products. Foreground EB correlations could bias measurements of β , and while thermal dust EB emission has been argued to be statistically nonzero, no evidence for synchrotron EB power has been reported. Unlike the dust-dominated Planck HFI maps, the majority of the LFI and WMAP polarization maps are instead dominated by synchrotron emission. Simultaneously constraining β and the polarization miscalibration angle, α , of each channel, we find a best-fit value of β  = 0.35° ±0.70° with LFI and WMAP data only. When including the Planck HFI PR4 maps, but fitting β separately for dust-dominated, β &gt; 70 GHz , and synchrotron-dominated channels, β ≤70 GHz , we find β ≤70 GHz  = 0.53° ±0.28°. This differs from zero with a statistical significance of 1.9 σ , and the main contribution to this value comes from the LFI 70 GHz channel. While the statistical significances of these results are low on their own, the measurement derived from the LFI and WMAP synchrotron-dominated maps agrees with the previously reported HFI-dominated constraints, despite the very different astrophysical and instrumental systematics involved in all these experiments.

• Eskilt, Johannes Røsok; Lee, Katherine; Watts, Duncan; Anshul, V.; Aurvik, Ragnhild & Basyrov, Artem [Show all 23 contributors for this article] (2023). COSMOGLOBE: Towards end-to-end CMB cosmological parameter estimation without likelihood approximations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 678. doi: 10.1051/0004-6361/202347358. Full text in Research Archive Show summary

  We implement support for a cosmological parameter estimation algorithm in Commander and quantify its computational efficiency and cost. For a semi-realistic simulation similar to Planck LFI 70 GHz, we find that the computational cost of producing one single sample is about 20 CPU-hours and that the typical Markov chain correlation length is ∼100 samples. The net effective cost per independent sample is ∼2000 CPU-hours, in comparison with all low-level processing costs of 812 CPU-hours for Planck LFI and WMAP in C OSMOGLOBE Data Release 1. Thus, although technically possible to run already in its current state, future work should aim to reduce the effective cost per independent sample by one order of magnitude to avoid excessive runtimes, for instance through multi-grid preconditioners and/or derivative-based Markov chain sampling schemes. This work demonstrates the computational feasibility of true Bayesian cosmological parameter estimation with end-to-end error propagation for high-precision CMB experiments without likelihood approximations, but it also highlights the need for additional optimizations before it is ready for full production-level analysis.

• Watts, Duncan; Basyrov, Artem; Eskilt, Johannes Røsok; Galloway, Mathew; Gjerløw, Eirik & Hergt, L.T. [Show all 33 contributors for this article] (2023). COSMOGLOBE DR1 results: I. Improved Wilkinson Microwave Anisotropy Probe maps through Bayesian end-to-end analysis. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 679. doi: 10.1051/0004-6361/202346414. Full text in Research Archive Show summary

  We present C OSMOGLOBE Data Release 1, which implements the first joint analysis of WMAP and Planck LFI time-ordered data, processed within a single Bayesian end-to-end framework. This framework directly builds on a similar analysis of the LFI measurements by the B EYOND P LANCK collaboration, and approaches the cosmic microwave background (CMB) analysis challenge through Gibbs sampling of a global posterior distribution, simultaneously accounting for calibration, mapmaking, and component separation. The computational cost of producing one complete WMAP+LFI Gibbs sample is 812 CPU-h, of which 603 CPU-h are spent on WMAP low-level processing; this demonstrates that end-to-end Bayesian analysis of the WMAP data is computationally feasible. We find that our WMAP posterior mean temperature sky maps and CMB temperature power spectrum are largely consistent with the official WMAP9 results. Perhaps the most notable difference is that our CMB dipole amplitude is 3366.2 ± 1.4 μK, which is 11 μK higher than the WMAP9 estimate and 2.5 σ higher than B EYOND P LANCK ; however, it is in perfect agreement with the HFI-dominated Planck PR4 result. In contrast, our WMAP polarization maps differ more notably from the WMAP9 results, and in general exhibit significantly lower large-scale residuals. We attribute this to a better constrained gain and transmission imbalance model. It is particularly noteworthy that the W -band polarization sky map, which was excluded from the official WMAP cosmological analysis, for the first time appears visually consistent with the V -band sky map. Similarly, the long standing discrepancy between the WMAP K -band and LFI 30 GHz maps is finally resolved, and the difference between the two maps appears consistent with instrumental noise at high Galactic latitudes. Relatedly, these updated maps allowed us for the first time to combine WMAP and LFI polarization data into a single coherent model of large-scale polarized synchrotron emission. Still, we identified a few issues that require additional work, including (1) low-level noise modeling; (2) large-scale temperature residuals at the 1–2 μK level; and (3) a strong degeneracy between the absolute K -band calibration and the dipole of the anomalous microwave emission component. We conclude that leveraging the complementary strengths of WMAP and LFI has allowed the mitigation of both experiments’ weaknesses, and resulted in new state-of-the-art WMAP sky maps. All maps and the associated code are made publicly available through the C OSMOGLOBE web page.

• Gerakakis, S.; Brilenkov, Maksym; Ieronymaki, M.; San, Metin; Watts, Duncan & Andersen, Kristian Joten [Show all 42 contributors for this article] (2023). From BeyondPlanck to Cosmoglobe: Open Science, Reproducibility, and Data Longevity. The Open Journal of Astrophysics. 6. doi: 10.21105/astro.2205.11262. Full text in Research Archive Show summary

  The BeyondPlanck and Cosmoglobe collaborations have implemented the first integrated Bayesian end-to-end analysis pipeline for CMB experiments. The primary long-term motivation for this work is to develop a common analysis platform that supports efficient global joint analysis of complementary radio, microwave, and sub-millimeter experiments. A strict prerequisite for this to succeed is broad participation from the CMB community, and two foundational aspects of the program are therefore reproducibility and Open Science. In this paper, we discuss our efforts toward this aim. We also discuss measures toward facilitating easy code and data distribution, community-based code documentation, user-friendly compilation procedures, etc. This work represents the first publicly released end-to-end CMB analysis pipeline that includes raw data, source code, parameter files, and documentation. We argue that such a complete pipeline release should be a requirement for all major future and publicly-funded CMB experiments, noting that a full public release significantly increases data longevity by ensuring that the data quality can be improved whenever better processing techniques, complementary datasets, or more computing power become available, and thereby also taxpayers’ value for money; providing only raw data and final products is not sufficient to guarantee full reproducibility in the future.

• Watts, Duncan; Galloway, Mathew; Ihle, Håvard Tveit; Andersen, Kristian Joten; Aurvik, Ragnhild & Banerji, Ranajoy [Show all 43 contributors for this article] (2023). From BeyondPlanck to Cosmoglobe: Preliminary WMAP Q-band analysis. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 675. doi: 10.1051/0004-6361/202243410. Full text in Research Archive Show summary

  We present the first application of the C OSMOGLOBE analysis framework by analyzing nine-year WMAP time-ordered observations that uses similar machinery to that of B EYOND P LANCK for the Planck Low Frequency Instrument (LFI). We analyzed only the Q -band (41 GHz) data and report on the low-level analysis process based on uncalibrated time-ordered data to calibrated maps. Most of the existing B EYOND P LANCK pipeline may be reused for WMAP analysis with minimal changes to the existing codebase. The main modification is the implementation of the same preconditioned biconjugate gradient mapmaker used by the WMAP team. Producing a single WMAP Q 1-band sample requires 22 CPU-hrs, which is slightly more than the cost of a Planck 44 GHz sample of 17 CPU-hrs; this demonstrates that a full end-to-end Bayesian processing of the WMAP data is computationally feasible. In general, our recovered maps are very similar to the maps released by the WMAP team, although with two notable differences. In terms of temperature, we find a ∼2 μK quadrupole difference that most likely is caused by different gain modeling, while in polarization we find a distinct 2.5 μK signal that has been previously referred to as poorly measured modes by the WMAP team. In the C OSMOGLOBE processing, this pattern arises from temperature-to-polarization leakage from the coupling between the CMB Solar dipole, transmission imbalance, and sidelobes. No traces of this pattern are found in either the frequency map or TOD residual map, suggesting that the current processing has succeeded in modeling these poorly measured modes within the assumed parametric model by using Planck information to break the sky-synchronous degeneracies inherent in the WMAP scanning strategy.

• Andersen, Kristian Joten; Aurvik, Ragnhild; Banerji, Ranajoy; Basyrov, Artem; Bersanelli, M. & Bertocco, S. [Show all 44 contributors for this article] (2023). BeyondPlanck: I. Global Bayesian analysis of the Planck Low Frequency Instrument data. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 675. doi: 10.1051/0004-6361/202244953. Full text in Research Archive Show summary

  We describe the B EYOND P LANCK project in terms of our motivation, methodology, and main products, and provide a guide to a set of companion papers that describe each result in more detail. Building directly on experience from ESA’s Planck mission, we implemented a complete end-to-end Bayesian analysis framework for the Planck Low Frequency Instrument (LFI) observations. The primary product is a full joint posterior distribution P ( ω  ∣  d ), where ω represents the set of all free instrumental (gain, correlated noise, bandpass, etc.), astrophysical (synchrotron, free-free, thermal dust emission, etc.), and cosmological (cosmic microwave background – CMB – map, power spectrum, etc.) parameters. Some notable advantages of this approach compared to a traditional pipeline procedure are seamless end-to-end propagation of uncertainties; accurate modeling of both astrophysical and instrumental effects in the most natural basis for each uncertain quantity; optimized computational costs with little or no need for intermediate human interaction between various analysis steps; and a complete overview of the entire analysis process within one single framework. As a practical demonstration of this framework, we focus in particular on low- ℓ CMB polarization reconstruction with Planck LFI. In this process, we identify several important new effects that have not been accounted for in previous pipelines, including gain over-smoothing and time-variable and non-1/ f correlated noise in the 30 and 44 GHz channels. Modeling and mitigating both previously known and newly discovered systematic effects, we find that all results are consistent with the ΛCDM model, and we constrained the reionization optical depth to τ  = 0.066 ± 0.013, with a low-resolution CMB-based χ 2 probability to exceed of 32%. This uncertainty is about 30% larger than the official pipelines, arising from taking a more complete instrumental model into account. The marginal CMB solar dipole amplitude is 3362.7 ± 1.4 μK, where the error bar was derived directly from the posterior distribution without the need of any ad hoc instrumental corrections. We are currently not aware of any significant unmodeled systematic effects remaining in the Planck LFI data, and, for the first time, the 44 GHz channel is fully exploited in the current analysis. We argue that this framework can play a central role in the analysis of many current and future high-sensitivity CMB experiments, including LiteBIRD, and it will serve as the computational foundation of the emerging community-wide C OSMOGLOBE effort, which aims to combine state-of-the-art radio, microwave, and submillimeter data sets into one global astrophysical model.

• Andersen, Kristian Joten; Herman, Daniel Christopher; Aurvik, Ragnhild; Banerji, Ranajoy; Basyrov, Artem & Bersanelli, M. [Show all 44 contributors for this article] (2023). BeyondPlanck: XIII. Intensity foreground sampling, degeneracies, and priors. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 675. doi: 10.1051/0004-6361/202243186. Full text in Research Archive Show summary

  We present the intensity foreground algorithms and model employed within the B EYOND P LANCK analysis framework. The B EYOND P LANCK analysis is aimed at integrating component separation and instrumental parameter sampling within a global framework, leading to complete end-to-end error propagation in the Planck Low Frequency Instrument (LFI) data analysis. Given the scope of the B EYOND P LANCK analysis, a limited set of data is included in the component separation process, leading to foreground parameter degeneracies. In order to properly constrain the Galactic foreground parameters, we improve upon the previous Commander component separation implementation by adding a suite of algorithmic techniques. These algorithms are designed to improve the stability and computational efficiency for weakly constrained posterior distributions. These are: (1) joint foreground spectral parameter and amplitude sampling, building on ideas from M IRAMARE ; (2) component-based monopole determination; (3) joint spectral parameter and monopole sampling; and (4) application of informative spatial priors for component amplitude maps. We find that the only spectral parameter with a significant signal-to-noise ratio using the current B EYOND P LANCK data set is the peak frequency of the anomalous microwave emission component, for which we find ν p  = 25.3 ± 0.5 GHz; all others must be constrained through external priors. Future works will be aimed at integrating many more data sets into this analysis, both map and time-ordered based, thereby gradually eliminating the currently observed degeneracies in a controlled manner with respect to both instrumental systematic effects and astrophysical degeneracies. When this happens, the simple LFI-oriented data model employed in the current work will need to be generalized to account for both a richer astrophysical model and additional instrumental effects. This work will be organized within the Open Science-based C OSMOGLOBE community effort.

• Cleary, Kieran A.; Borowska, Jowita; Breysse, Patrick C.; Catha, Morgan; Chung, Dongwoo T. & Church, Sarah E. [Show all 43 contributors for this article] (2022). COMAP Early Science. I. Overview. The Astrophysical Journal (ApJ). ISSN 0004-637X. 933(2). doi: 10.3847/1538-4357/ac63cc. Full text in Research Archive Show summary

  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 deg2 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 PCO(k) = −2.7 ± 1.7 × 104 μK2 Mpc3 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 ${\left\langle {Tb}\right\rangle }^{2}\lt 49$ μK2, 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.

• Foss, Marie Kristine; Ihle, Håvard Tveit; Borowska, Jowita; Cleary, Kieran A.; Eriksen, Hans Kristian Kamfjord & Harper, Stuart E. [Show all 33 contributors for this article] (2022). COMAP Early Science. III. CO Data Processing. The Astrophysical Journal (ApJ). ISSN 0004-637X. 933(2). doi: 10.3847/1538-4357/ac63ca. Full text in Research Archive Show summary

  We describe the first-season CO Mapping Array Project (COMAP) analysis pipeline that converts raw detector readouts to calibrated sky maps. This pipeline implements four main steps: gain calibration, filtering, data selection, and mapmaking. Absolute gain calibration relies on a combination of instrumental and astrophysical sources, while relative gain calibration exploits real-time total-power variations. High-efficiency filtering is achieved through spectroscopic common-mode rejection within and across receivers, resulting in nearly uncorrelated white noise within single-frequency channels. Consequently, near-optimal but biased maps are produced by binning the filtered time stream into pixelized maps; the corresponding signal bias transfer function is estimated through simulations. Data selection is performed automatically through a series of goodness-of-fit statistics, including χ2 and multiscale correlation tests. Applying this pipeline to the first-season COMAP data, we produce a data set with very low levels of correlated noise. We find that one of our two scanning strategies (the Lissajous type) is sensitive to residual instrumental systematics. As a result, we no longer use this type of scan and exclude data taken this way from our Season 1 power spectrum estimates. We perform a careful analysis of our data processing and observing efficiencies and take account of planned improvements to estimate our future performance. Power spectrum results derived from the first-season COMAP maps are presented and discussed in companion papers.

• Lamb, James W.; Cleary, Kieran A.; Woody, David P.; Catha, Morgan; Chung, Dongwoo T. & Gundersen, Joshua Ott [Show all 36 contributors for this article] (2022). COMAP Early Science. II. Pathfinder Instrument. The Astrophysical Journal (ApJ). ISSN 0004-637X. 933(2). doi: 10.3847/1538-4357/ac63c6. Full text in Research Archive Show summary

  Line intensity mapping (LIM) is a new technique for tracing the global properties of galaxies over cosmic time. Detection of the very faint signals from redshifted carbon monoxide (CO), a tracer of star formation, pushes the limits of what is feasible with a total-power instrument. The CO Mapping Project Pathfinder is a first-generation instrument aiming to prove the concept and develop the technology for future experiments, as well as delivering early science products. With 19 receiver channels in a hexagonal focal plane arrangement on a 10.4 m antenna and an instantaneous 26–34 GHz frequency range with 2 MHz resolution, it is ideally suited to measuring CO (J = 1–0) from z ∼ 3. In this paper we discuss strategies for designing and building the Pathfinder and the challenges that were encountered. The design of the instrument prioritized LIM requirements over those of ancillary science. After a couple of years of operation, the instrument is well understood, and the first year of data is already yielding useful science results. Experience with this Pathfinder will guide the design of the next generations of experiments.

• Rennie, Thomas J.; Harper, Stuart E.; Dickinson, Clive; Philip, Liju; Cleary, Kieran A. & Bond, Richard J. [Show all 32 contributors for this article] (2022). COMAP Early Science. VI. A First Look at the COMAP Galactic Plane Survey. The Astrophysical Journal (ApJ). ISSN 0004-637X. 933(2). doi: 10.3847/1538-4357/ac63c8. Full text in Research Archive Show summary

  We present early results from the CO Mapping Array Project (COMAP) Galactic Plane Survey conducted between 2019 June and 2021 April, spanning 20° < ℓ < 40° in Galactic longitude and ∣b∣ < 1fdg5 in Galactic latitude with an angular resolution of 4farcm5. We present initial results from the first part of the survey, including the diffuse emission and spectral energy distributions of H ii regions and supernova remnants (SNRs). Using low- and high-frequency surveys to constrain free–free and thermal dust emission contributions, we find evidence of excess flux density at 30 GHz in six regions, which we interpret as anomalous microwave emission. Furthermore we model ultracompact H ii contributions using data from the 5 GHz CORNISH catalog and reject these as the cause of the 30 GHz excess. Six known SNRs are detected at 30 GHz, and we measure spectral indices consistent with the literature or show evidence of steepening. The flux density of the SNR W44 at 30 GHz is consistent with a power-law extrapolation from lower frequencies with no indication of spectral steepening in contrast with recent results from the Sardinia Radio Telescope. We also extract five hydrogen radio recombination lines (RRLs) to map the warm ionized gas, which can be used to estimate electron temperatures or to constrain continuum free–free emission. The full COMAP Galactic Plane Survey, to be released in 2023/2024, will span ℓ ∼ 20°–220° and will be the first large-scale radio continuum and RRL survey at 30 GHz with 4farcm5 resolution.

• Breysse, Patrick C.; Chung, Dongwoo T.; Cleary, Kieran A.; Ihle, Håvard Tveit; Padmanabhan, Hamsa & Silva, Marta Bruno [Show all 32 contributors for this article] (2022). COMAP Early Science. VII. Prospects for CO Intensity Mapping at Reionization. The Astrophysical Journal (ApJ). ISSN 0004-637X. 933(2). doi: 10.3847/1538-4357/ac63c9. Full text in Research Archive Show summary

  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-EoR supplements 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 the z ∼ 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-EoR measurement. 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-EoR can make a detailed measurement of the cosmic molecular gas history from z ∼ 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.

• Chung, Dongwoo T.; Breysse, Patrick C.; Cleary, Kieran A.; Ihle, Håvard Tveit; Padmanabhan, Hamsa & Silva, Marta Bruno [Show all 37 contributors for this article] (2022). COMAP Early Science. V. Constraints and Forecasts at z ∼3. The Astrophysical Journal (ApJ). ISSN 0004-637X. 933(2). doi: 10.3847/1538-4357/ac63c7. Full text in Research Archive Show summary

  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 Aclust ≲ 70 μK2 greatly improves on the indirect upper limit of 420 μK2 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, ${\left\langle {Tb}\right\rangle }_{2}$ ≲ 50 μK2, and the cosmic molecular gas density, ρH2 < 2.5 × 108 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.

• Ihle, Håvard Tveit; Borowska, Jowita; Cleary, Kieran A.; Eriksen, Hans Kristian Kamfjord; Foss, Marie Kristine & Harper, Stuart E. [Show all 33 contributors for this article] (2022). COMAP Early Science. IV. Power Spectrum Methodology and Results. The Astrophysical Journal (ApJ). ISSN 0004-637X. 933(2). doi: 10.3847/1538-4357/ac63c5. Full text in Research Archive Show summary

  We present the power spectrum methodology used for the first-season COMAP analysis, and assess the quality of the current data set. The main results are derived through the Feed–Feed Pseudo-Cross-Spectrum (FPXS) method, which is a robust estimator with respect to both noise modeling errors and experimental systematics. We use effective transfer functions to take into account the effects of instrumental beam smoothing and various filter operations applied during the low-level data processing. The power spectra estimated in this way have allowed us to identify a systematic error associated with one of our two scanning strategies, believed to be due to residual ground or atmospheric contamination. We omit these data from our analysis and no longer use this scanning technique for observations. We present the power spectra from our first season of observing, and demonstrate that the uncertainties are integrating as expected for uncorrelated noise, with any residual systematics suppressed to a level below the noise. Using the FPXS method, and combining data on scales k = 0.051–0.62 Mpc−1, we estimate PCO(k) = −2. 7 ± 1.7 × 104 μK2 Mpc3, the first direct 3D constraint on the clustering component of the CO(1–0) power spectrum in the literature.

• Chung, Dongwoo T.; Breysse, Patrick C.; Ihle, Håvard Tveit; Padmanabhan, Hamsa; Silva, Marta Bruno & Bond, John Richard [Show all 18 contributors for this article] (2021). A Model of Spectral Line Broadening in Signal Forecasts for Line-intensity Mapping Experiments. The Astrophysical Journal (ApJ). ISSN 0004-637X. 923(2). doi: 10.3847/1538-4357/ac2a35. Full text in Research Archive

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• Lunde, Jonas Gahr Sturtzel (2026). Mapping the large-scale Universe with COMAP and Commander4. Universitetet i Oslo. Full text in Research Archive Show summary

  Line Intensity Mapping (LIM) is an emerging observational field in astronomy, aiming to provide a more complete and unbiased picture of the Universe across vast cosmic space and time. It does this by measuring the diffuse emission from various gases in the Universe. The primary contribution of this thesis is improved analysis methods for the CO Mapping Array Project (COMAP), a LIM experiment targeting emission from star-forming carbon monoxide gas 11-12 billion years ago, during the Epoch of Galaxy Assembly. The CO signal is incredibly faint and must be disentangled from signal contaminations, both from the sky and the instrument itself. This thesis discusses how systematic errors in the petabyte-sized COMAP dataset can be handled efficiently and robustly. This effort culminated in the COMAP Season 2 results, which improved upon existing constraints of the cosmic CO signal by an order of magnitude, bringing COMAP closer to the world's first detection of this faint signal. Many similar data analysis challenges are also encountered in observations of the Cosmic Microwave Background (CMB). This thesis also contributes to the CMB field by introducing a prototype of Commander4, a massively parallel Gibbs sampling software aimed at high-precision analysis of current and future CMB datasets.

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