Measurements of the HI intensity mapping power spectrum at low redshifts with MIGHTEE data: comparison with detected HI galaxies

Abstract

Line intensity mapping provides a statistical approach to tracing the large-scale distribution of matter in the Universe. We apply the HI intensity mapping technique to interferometric data from the MeerKAT International GHz-Tiered Extragalactic Explorations (MIGHTEE) Survey, analysing 17.5 hours of a single pointing in the COSMOS field, using a 60 MHz sub-band in the frequency range 1332 - 1392 MHz ($0.02\lesssim z\lesssim 0.07$). Using a delay-spectrum-based estimator, we measure the HI power spectrum on sub-megaparsec scales and compare it directly to the power spectrum inferred from a catalogue of individually detected HI galaxies in the same field. After mitigating low-level broadband contamination through conservative outlier flagging in the three-dimensional power spectrum, cross-correlation of time-split visibilities yields a statistically significant detection on scales $3\lesssim k\lesssim 20{\mathrm{Mpc}}^{-1}$ with a total signal-to-noise ratio of $\sim 13$. Over this range, the power spectra obtained from visibilities and detected galaxies are consistent within uncertainties and have comparable amplitudes of order $10^{-2}$ - $10^{-1}$ ${\mathrm{mK}}^2{\mathrm{Mpc}}^3$. End-to-end validation is performed by propagating detected galaxies through the power spectrum estimator via both direct intensity-field construction and simulated visibilities, demonstrating agreement up to $k\sim 20{\mathrm{Mpc}}^{-1}$, beyond which measurements become noise-dominated. A statistically significant correlation is also observed between the data and the simulated visibilities from the detected HI galaxies, which should be free of systematics. These results provide a self-consistent validation of interferometric HI intensity mapping at low redshift and demonstrate agreement with galaxy-based measurements within the same cosmological volume.

20 pages, 25 figures, 3 tables. Submitted to MNRAS and comments are welcome