COMAP Pathfinder -- Season 2 results I. Improved data selection and processing

Abstract

The CO Mapping Array Project (COMAP) Pathfinder is performing line intensity mapping of CO emission to trace the distribution of unresolved galaxies at redshift $z\sim 3$. We present an improved version of the COMAP data processing pipeline and apply this 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. Secondly, 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 has 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. On the other hand, due to the increased sensitivity, two new pointing-correlated systematic errors have emerged, and we introduce a new map-domain PCA filter to suppress these. Subtracting only 5 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 these improvements, we find that each hour of raw Season 2 observations yields on average 3.2 times more cleaned data compared to 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 8 higher than in ES. The resulting maps have reached an uncertainty of $25$-$50\mu K$ per voxel, providing by far the strongest constraints on cosmological CO line emission published to date.

22 pages, 22 figures, 2 tables, v3 reflects changes made for version accepted and published by Astronomy and Astrophysics, no change to final results

References in corpus (27)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Correcting systematic effects in a large set of photometric lightcurves
• Measurement of 21 cm brightness fluctuations at z ~ 0.8 in cross-correlation
• Intensity Mapping with Carbon Monoxide Emission Lines and the Redshifted 21 cm Line
• Lack of clustering in low-redshift 21-cm intensity maps cross-correlated with 2dF galaxy densities
• Connecting CO Intensity Mapping to Molecular Gas and Star Formation in the Epoch of Galaxy Assembly
• The mass-Peak Patch algorithm for fast generation of deep all-sky dark matter halo catalogues and its N-Body validation
• Cross-correlations as a cosmological carbon monoxide detector
• A wide field-of-view low-resolution spectrometer at APEX: instrument design and science forecast
• Carbon Monoxide Intensity Mapping at Moderate Redshifts
• COMAP Early Science: I. Overview
• Making CMB temperature and polarization maps with Madam
• COMAP Early Science: V. Constraints and Forecasts at $z\sim 3$
• SPT-SLIM: A Line Intensity Mapping Pathfinder for the South Pole Telescope
• COMAP Early Science: VII. Prospects for CO Intensity Mapping at Reionization
• COMAP Early Science: IV. Power Spectrum Methodology and Results
• A model of spectral line broadening in signal forecasts for line-intensity mapping experiments
• COMAP Early Science: II. Pathfinder Instrument
• COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
• COMAP Early Science: III. CO Data Processing
• Extragalactic Science with the Experiment for Cryogenic Large-aperture Intensity Mapping
• COMAP Pathfinder -- Season 2 results II. Updated constraints on the CO(1-0) power spectrum
• COMAP Pathfinder -- Season 2 results III. Implications for cosmic molecular gas content at "Cosmic Half-past Eleven"

Cited by in corpus (6)

• COMAP Pathfinder -- Season 2 results II. Updated constraints on the CO(1-0) power spectrum
• Three-Dimensional Stacking as a Line Intensity Mapping Statistic
• COMAP Pathfinder -- Season 2 results III. Implications for cosmic molecular gas content at "Cosmic Half-past Eleven"
• COMAP Pathfinder -- Season 2 results IV. A stack on eBOSS/DESI quasars
• CosmoGLINT: Cosmological Generative Model for Line Intensity Mapping with Transformer
• Constraining the [CII] luminosity function from the power spectrum of line-intensity maps at redshift 3.6