MeerKLASS L-band deep-field intensity maps: entering the H <scp>i</scp> dominated regime

Abstract

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.