Hi intensity mapping with MeerKAT: A measurement of the 21-cm auto-spectrum on cosmological scales
Year: 2026
Type: article
Abstract: We report a direct measurement of the 21-cm signal from neutral hydrogen (Hi) via the intensity mapping technique at redshift z = 0.42 through its power spectrum at cosmological scales 0.095 h Mpc−1 < k < 0.245 h Mpc−1. We analyse intensity maps observed in the frequency range 971.2 MHz < ν < 1023.6 MHz during the 2021 observational campaign of the MeerKAT Large Area Synoptic Survey (MeerKLASS) spanning an area of approximately 236 °2. Capitalising on the depth of this survey, we divide the data set into multiple observationally independent subsets. After performing blind contaminant separation independently on each subset, we exploit internal cross-correlations to suppress the instrumental noise plateau and isolate the cosmological signal from residual systematics. Although the subsets’ auto-spectra show the presence of excess power that we deem linked to still unresolved systematics, the cross-spectra measurements satisfactorily pass a battery of null and robustness tests. We introduce a multi-subset formalism to infer the amplitude of the Hi auto-spectrum from our internal cross-spectra measurements while marginalising the potential signal loss that occurs during data processing, reaching a detection with signal-to-noise ratio of 6.2. We constrain the clustering amplitude of the signal in terms of the Hi cosmic abundance and its linear bias, measuring 103 ΩHibHi = $1.271{_{-0.598}^{+1.080}}$. This direct measurement marks a milestone in demonstrating the effectiveness of the Hi intensity mapping technique for future surveys with the SKA Observatory, of which MeerKAT is a precursor.
Institutions: University of Milan, Brera Astronomical Observatory, Istituto Nazionale di Fisica Nucleare, Sezione di Milano, University of Turin, National Institute for Astrophysics, Instituto de Física de Cantabria, University of Manchester, University of the Western Cape, Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Osservatorio Astrofisico di Torino, Trieste Astronomical Observatory, Institute for Fundamental Physics of the Universe, Royal Observatory, University of Edinburgh, University of Portsmouth, Universidade do Porto, Institute of Astrophysics and Space Sciences, Centro de Astrofísica da Universidade do Porto, Chinese Academy of Sciences, National Astronomical Observatories, University of Cambridge, Northeastern University, South African Radio Astronomy Observatory, Lagrange Laboratory, Observatoire de la Côte d’Azur, Shanghai Astronomical Observatory
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
OpenAlex ID: W7222779501