2025MNRAS.541..476M

We 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 $\sim$ 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 $0.5\, \textrm {Mpc}^{-1} \lesssim k \lesssim 10\, \textrm {Mpc}^{-1}$ 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 mK$^{2}$ Mpc${^3}$ from the 2$\sigma$ cross-correlation measurements and 25.82 mK$^{2}$ Mpc${^3}$ from autocorrelation at $k\sim$2 Mpc$^{-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.