Probing Cosmology with the MeerKAT Interferometer

Abstract

Intensity mapping is a novel technique that has provided significant insights into the large-scale structure of the Universe. This thesis investigates the use of the Hi intensity mapping technique with data from the MeerKAT International GHzTiered Extragalactic Explorations (MIGHTEE) Survey. In particular, 17.45 hours of data on the COSMOS field is used to measure the Hi power spectrum signal in the Early Science frequency range of 1310- 1420 MHz, in a sub-band of 60 MHz spanning a redshift range of 0.02 ≤ z ≤ 0.066, corresponding to 1332 MHz ≤ ν ≤ 1392 MHz. 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 of the H i power spectrum signal on scales 3 ≲ k ≲ 20 Mpc−1, with a total signal-to-noise ratio of ∼ 13. This is compared to the Hi power spectrum signal obtained on the detected Hi galaxies on the same field and over the same redshift range from a catalogue created with this MIGHTEE data. This is done to test how well the Hi intensity mapping technique can recover the Hi content in the COSMOS field and to test whether or not the Hi galaxy catalogue constrains all the Hi content in this specific volume of the sky. Pipelines for visibility data processing, converting the Hi galaxy detections into an intensity map, and power spectrum estimation are developed in this work. The same procedures for contamination flagging and estimated thermal noise weighting are applied to the resulting power spectra from both data sets to ensure we are comparing the same estimator result. On the k scales of interest, 3 ≲ k ≲ 20 Mpc−1, the Hi power spectra estimated on these data sets are consistent within the same orders of magnitude (∼ 10−2- 10−1 Mpc3 mK2), and within 1–2 σ uncertainties of each of the two estimated power spectra. A statistically significant correlation is also observed between the visibility data and simulated visibilities, which use the detected Hi galaxies as input, and 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.