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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

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

  • MeerKLASS Collaboration
  • Matilde Barberi-Squarotti1,2,3,4
  • José L Bernal5
  • Philip Bull6,7
  • Stefano Camera4,8,9,7
  • Isabella P Carucci10,11
  • Zhaoting Chen12
  • Steven Cunnington13,6
  • Brandon N Engelbrecht7
  • José Fonseca7,14,15
  • Keith Grainge6
  • Wenkai Hu16,7
7 more authors
  • Melis O Irfan17,7
  • Yichao Li18,7
  • Mário G Santos7,19
  • Marta Spinelli20,7
  • Jingying Wang21,7
  • Amadeus Witzemann7,6
  • Laura Wolz6
21 affiliations
  1. 1Dipartimento di Fisica, Università degli Studi di Milano , via G. Celoria 16, 20133 Milano ,
  2. 2INFN - Istituto Nazionale di Fisica Nucleare, Sezione di Milano , via G. Celoria 16, 20133 Milano ,
  3. 3INAF – Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Brera-Merate , via Brera 28, 20121 Milano ,
  4. 4Dipartimento di Fisica, Università degli Studi di Torino , via P. Giuria 1, 10125 Torino ,
  5. 5Instituto de Física de Cantabria (IFCA), CSIC-Univ. de Cantabria , Avda. de los Castros s/n, E-39005 Santander ,
  6. 6Jodrell Bank Centre for Astrophysics, Department of Physics, and Astronomy, The University of Manchester , Manchester M13 9PL ,
  7. 7Department of Physics & Astronomy, University of the Western Cape , Robert Sobukwe Road, Cape Town 7535 ,
  8. 8INFN - Istituto Nazionale di Fisica Nucleare, Sezione di Torino , via P. Giuria 1, 10125 Torino ,
  9. 9INAF - Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino , 10025 Pino Torinese ,
  10. 10INAF – Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Trieste , Via G.B. Tiepolo 11, 34131 Trieste ,
  11. 11IFPU – Institute for Fundamental Physics of the Universe , Via Beirut 2, 34151 Trieste ,
  12. 12Institute for Astronomy, The University of Edinburgh, Royal Observatory , Edinburgh EH9 3HJ ,
  13. 13Institute of Cosmology & Gravitation, University of Portsmouth , Dennis Sciama Building, Portsmouth, PO1 3FX ,
  14. 14Instituto de Astrofísica e Ciências do Espaço , Universidade do Porto CAUP, 4150-762 Porto ,
  15. 15Departamento de Física e Astronomia, Faculdade de Ciências , Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto ,
  16. 16State Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories , Chinese Academy of Sciences, Beijing 100101 ,
  17. 17Institute of Astrophysics, University of Cambridge , Madingley Road, CB3 0HA
  18. 18Department of Physics, College of Sciences, Northeastern University , Wenhua Road, Shenyang 11089 ,
  19. 19South African Radio Astronomy Observatory (SARAO) , Liesbeek House, Cape Town, 7700 ,
  20. 20Observatoire de la Côte d’Azur, Laboratoire Lagrange , Bd de l’Observatoire, CS 34229, 06304 Nice cedex 4 ,
  21. 21State Key Laboratory of Radio Astronomy and Technology, Shanghai Astronomical Observatory , CAS, 80 Nandan Road, Shanghai 200030 ,
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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.

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Cite

BibTeXRIS
BibTeX
@article{collaboration2026intensity,
  title = {{Hi intensity mapping with MeerKAT: A measurement of the 21-cm auto-spectrum on cosmological scales}},
  author = {MeerKLASS Collaboration and 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},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = nov,
  doi = {10.1093/mnras/stag1911},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1911/9011414},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Hi intensity mapping with MeerKAT: A measurement of the 21-cm auto-spectrum on cosmological scales
AU  - MeerKLASS Collaboration
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  - 2026/11/03
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1911
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1911/9011414
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 °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.
SN  - 0035-8711
SN  - 1365-2966
ER  -