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

TL;DR

This study uses MeerKAT MIGHTEE data to measure the HI intensity mapping power spectrum at low redshifts, validating the technique by comparing it with galaxy detections and simulations, achieving significant detection on small scales.

Contribution

First application of HI intensity mapping with MeerKAT data to measure the power spectrum at low redshift, validated against galaxy catalogues and simulations.

Findings

Significant detection of HI power spectrum at scales 3-20 Mpc^{-1} with SNR ~13

Power spectra from visibilities and galaxy catalogues are consistent within uncertainties

Validation of intensity mapping technique through simulations and cross-correlation

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.