Taylor, RussSantos, Mario G.Townsend, JunaidTaylor, Russ2025-11-272025-11-272025Mazumder, A., Wolz, L., Chen, Z., Paul, S., Santos, M.G., Jarvis, M., Townsend, J., Sekhar, S. and Taylor, R., 2025. HI Intensity Mapping with the MIGHTEE Survey: First Results of the H i Power Spectrum. Monthly Notices of the Royal Astronomical Society, p.staf975.https://doi.org/10.1093/mnras/staf975https://doi.org/10.1093/mnras/staf975https://hdl.handle.net/10566/21483We present the first results of the H I intensity mapping power spectrum analysis with the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) survey. We use data covering ∼ 4 square degrees in the COSMOS field using a frequency range of 962.5–1008.42 MHz, equivalent to H I emission in 0.4 < z < 0.48. The data consist of 15 pointings with a total of 94.2 h on-source. We verify the suitability of the MIGHTEE data for H I intensity mapping by testing for residual systematics across frequency, baselines, and pointings. We also vary the window used for H I signal measurements and find no significant improvement using stringent Fourier mode cuts. We compute the H I power spectrum at scales 0.5 Mpc−1 ≾ k ≾ 10 Mpc−1 in autocorrelation as well as cross-correlation between observational scans using power spectrum domain averaging for pointings. We report consistent upper limits of 29.8 mK2 Mpc3 from the 2σ cross-correlation measurements and 25.82 mK2 Mpc3 from autocorrelation at k ∼2 Mpc−1.The low signal-to-noise ratio in this data potentially limits our ability to identify residual systematics, which will be addressed in the future by incorporating more data in the analysis.encosmology: observationslarge-scale structure of Universeradio lines: galaxiestechniques: interferometricH I intensityArticle