https://doi.org/10.1140/epjc/s10052-025-14241-7
Regular Article - Theoretical Physics
Constraining primordial non-Gaussianity by combining photometric galaxy and 21 cm intensity mapping surveys
1
Department of Physics and Astronomy, University of the Western Cape, 7535, Cape Town, South Africa
2
Department of Physics, Stellenbosch University, 7602, Matieland, South Africa
3
Institute of Cosmology and Gravitation, University of Portsmouth, PO1 3FX, Portsmouth, UK
4
National Institute for Theoretical and Computational Sciences (NITheCS), 7535, Cape Town, South Africa
Received:
21
February
2025
Accepted:
25
April
2025
Published online:
14
May
2025
The fluctuations produced during cosmic inflation may exhibit non-Gaussian characteristics that are imprinted in the large-scale structure of the Universe. This non-Gaussian imprint is an ultra-large scale signal that can be detected using the power spectrum. We focus on the local-type non-Gaussianity 
and employ a multi-tracer analysis that combines different probes in order to mitigate cosmic variance and maximize the non-Gaussian signal. In our previous paper, we showed that combining spectroscopic galaxy surveys with 21 cm intensity mapping surveys in interferometer mode could lead to a 
20–30% improvement in the precision on this non-Gaussian signal. Here we combine the same 21 cm experiments, including also single-dish surveys, with photometric galaxy surveys. The 21 cm single-dish surveys are based on MeerKAT and SKAO and the interferometric surveys are alike to HIRAX and PUMA. We implement foreground-avoidance filters and utilize models for the 21 cm thermal noise associated with single-dish and interferometer modes. The photometric galaxy surveys are similar to the DES and LSST. Our multi-tracer Fisher forecasts show a better precision for the combination of the photometric galaxy surveys and 21 cm interferometric surveys than with the 21 cm single-dish surveys – leading to at most an improvement of 
in the former case and 
in the latter case. Furthermore, we examine the impact of varying the foreground filter parameter, redshift range and sky area on the derived constraint. We find that the constraint is highly sensitive to both the redshift range and sky area. The foreground filter parameter shows negligible effect.
© The Author(s) 2025
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Funded by SCOAP3.
