article · Monthly Notices of the Royal Astronomical Society
This research details the deepest single-dish neutral hydrogen intensity maps recorded to date, produced during the final L-band observations of the MeerKAT Large Area Synoptic Survey. Using 64 dishes across 41 repeated scans over a 236 square degree field, the survey compiled 62 hours of observational data per dish. An iterative self-calibration technique constrained the thermal noise of the resulting maps to roughly 1.21 millikelvin, which is approximately 1.2 times the theoretical limit. At this level, thermal noise is lower than the neutral hydrogen fluctuations on large scales. The study establishes an upgraded analysis pipeline to handle the necessary covariance estimations, validating the methodology with simulations and optical data from the Galaxy And Mass Assembly survey. Cross-correlation with over two thousand galaxies yielded a detection exceeding four sigma, alongside the first evidence of neutral hydrogen emission from stacking MeerKAT single-dish maps at galaxy positions.
Mapping the large-scale distribution of neutral hydrogen is essential for understanding how cosmic structures and galaxies evolve across the universe. By pushing single-dish radio measurements to unprecedented sensitivity, this work shows that background noise can be suppressed enough to reveal faint cosmological signals directly, validating new calibration tools needed for modern, large-scale astronomical surveys.
The abstract does not indicate an application pathway, as it focuses entirely on early-stage fundamental astrophysics and observational radio astronomy techniques.
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ABSTRACT We present results from MeerKAT single-dish H i intensity maps, the final observations to be performed in L-band in the MeerKAT Large Area Synoptic Survey (MeerKLASS) campaign. The observations represent the deepest single-dish H i intensity maps to date, produced from 41 repeated scans over $236\, \deg ^2$, providing 62 h of observational data for each of the 64 dishes before flagging. By introducing an iterative self-calibration process, the estimated thermal noise of the reconstructed maps is limited to ${\sim }\, 1.21$ mK ($1.2\, \times$ the theoretical noise level). This thermal noise will be subdominant relative to the H i fluctuations on large scales ($k\, {\lesssim }\, 0.15\, h\, \text{Mpc}^{-1}$), which demands upgrades to power spectrum analysis techniques, particularly for covariance estimation. In this work, we present the improved MeerKLASS analysis pipeline, validating it on both a suite of mock simulations and a small sample of overlapping spectroscopic galaxies from the Galaxy And Mass Assembly (GAMA) survey. Despite only overlapping with ${\sim }\, 25~{{\ \rm per\ cent}}$ of the MeerKLASS deep field, and a conservative approach to covariance estimation, we still obtain a ${\gt }\, 4\, \sigma$ detection of the cross-power spectrum between the intensity maps and the 2269 galaxies at the narrow redshift range $0.39\, {\lt }\, z\, {\lt }\, 0.46$. We briefly discuss the H i autopower spectrum from these data, the detection of which will be the focus of follow-up work. For the first time with MeerKAT single-dish intensity maps, we also present evidence of H i emission from stacking the maps onto the positions of the GAMA galaxies.
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DOI: 10.1093/mnras/staf195
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