HI intensity mapping with MeerKAT: A measurement of the 21-cm auto-spectrum on cosmological scales

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 deg². 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 Ω_HI b_HI=1.271^+1.080_−0.598. 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.

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BibTeX RIS

BibTeX

@misc{barberisquarotti2026intensity,
  title = {{HI intensity mapping with MeerKAT: A measurement of the 21-cm auto-spectrum on cosmological scales}},
  author = {Matilde Barberi-Squarotti and José L Bernal and Philip Bull and Stefano Camera and Isabella P Carucci and Zhaoting Chen and Steven Cunnington and Brandon N Engelbrecht and José Fonseca and Keith Grainge and Wenkai Hu and Melis O Irfan and Yichao Li and Mário G Santos and Marta Spinelli and Jingying Wang and Amadeus Witzemann and Laura Wolz},
  howpublished = {HAL},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.12158},
  eprint = {2610.12158},
  archivePrefix = {arXiv},
  url = {https://hal.science/hal-05842227v1},
}

RIS

TY  - UNPB
TI  - HI intensity mapping with MeerKAT: A measurement of the 21-cm auto-spectrum on cosmological scales
AU  - Matilde Barberi-Squarotti
AU  - José L Bernal
AU  - Philip Bull
AU  - Stefano Camera
AU  - Isabella P Carucci
AU  - Zhaoting Chen
AU  - Steven Cunnington
AU  - Brandon N Engelbrecht
AU  - José Fonseca
AU  - Keith Grainge
AU  - Wenkai Hu
AU  - Melis O Irfan
AU  - Yichao Li
AU  - Mário G Santos
AU  - Marta Spinelli
AU  - Jingying Wang
AU  - Amadeus Witzemann
AU  - Laura Wolz
PY  - 2026
DA  - 2026/10/08
PB  - HAL
DO  - 10.48550/arxiv.2610.12158
UR  - https://hal.science/hal-05842227v1
AB  - 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 deg^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 10^3 Ω_HI b_HI=1.271^+1.080_−0.598. 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.
ER  -

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