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.

Figures (23)

• Figure 1: The $uv$ distribution of the combined COSMOS field data used in this study at the central frequency of 1362.425 MHz. This distribution is shown in 2D, with the number of $uv$ points displayed in the colour bar. The grid size used here is $\Delta u = \Delta v = 73\lambda$, where $\lambda$ is the central wavelength of the band used in this study.
• Figure 2: The HI masses, $M_{\ion{H}{I}}$, for the selected galaxies from the full MIGHTEE-HI Early Science catalogue plotted at their respective redshifts, $z$. The sample shown contains galaxies on the central COSMOS pointing only and is sourced over a redshift range that aligns with the frequency range chosen for the visibility data.
• Figure 3: The HI masses, $M_{\ion{H}{I}}$, and positions for each galaxy selected in the sub-band from the catalogue in R.A. and Dec. The dashed circle corresponds to the main lobe of the MeerKAT primary beam at 1362.425 MHz, while the dotted square denotes the edges along the Right Ascension and Declination maximum and minimum limits of the box in which the galaxy masses are placed (see Section \ref{['section:hi_gal_pspec']}).
• Figure 4: The Stokes I cylindrical cross-correlation (left) and auto-correlation (right) power spectra of the combined 17.45h of MIGHTEE COSMOS Early Science visibility data before any contamination removal is applied to the 3D power spectrum cube, $P(\boldsymbol{k}_{\perp}, k_{\parallel})$. Also shown is the horizon limit, $k_{\parallel}^{\text{horizon}}(k_{\perp})$ as a dashed grey line for $\pm k_{\parallel}$.
• Figure 5: Comparison between the Stokes V and refitted simulated thermal noise 1D auto-power spectra. The increased amplitude we observe at $k \lesssim 10$ Mpc$^{-1}$ for Stokes V is primarily due to leakage from Stokes I, resulting in the discrepancy in the two power spectra. Beyond this, the power spectra are consistent across all $k$ scales.