Neutral hydrogen intensity mapping with MeerKAT a novel way to explore the Universe

A sky map derived using MeerKAT single dish mode. Our Galaxy contributes most of the emission. The magenta dots label the positions of bright radio point sources. CREDIT: MEERKLASS team

MeerKAT and the forthcoming SKA telescopes are large arrays aiming to solve a series of exciting science problems including some of the most fundamental questions about the Universe.

A recent paper led by postdoctoral researcher Dr Jingying Wang from the Centre for Radio Cosmology (CRC) at the University of the Western Cape, South Africa, demonstrates the possibility to push the boundaries of astrophysics and cosmology using MeerKAT’s 64 dishes and an innovative technique called “neutral hydrogen intensity mapping”.

Neutral hydrogen (abbreviated as HI) can be found all over the Universe. It emits radio waves at a distinctive wavelength – 21 centimetres – that can be captured by radio telescopes such as MeerKAT and the SKA telescopes. The expansion of space causes this wavelength to stretch over time (known as redshift), allowing us to infer how long ago the radio waves were emitted through their detected wavelength. Mapping the HI distribution across cosmic time promises to provide valuable new insights into astrophysics and cosmology.

With the full array of 64 dishes now fully operational, MeerKAT should be able to measure the distribution of HI on very large scales. In order to do so, MeerKAT has to be used in the so-called single-dish mode (instead of using the more traditional cross-correlations between dishes), which allows it to scan large enough volumes of the sky extremely rapidly. This in turn will allow us to produce the largest 3D maps of the Universe and probe the nature of the mysterious dark energy.

Under the leadership of Prof. Mario Santos, pilot surveys with MeerKAT are already underway. The 64 dishes of MeerKAT were employed to finish seven observations(of two hours each) and have produced 8.4TB of raw data.

As a first step towards demonstrating the potential power of the HI intensity mapping technique, Dr Wang and collaborators showed that with their newly developed pipeline for data calibration, they are able to compensate for instrumental and environmental effects in order to recover useful scientific data. Although the observations suffer from human-made radio frequency interference, the researchers successfully calibrated and reconstructed 3D celestial data cubes (across the sky and along frequency) for the sky in this pilot study.

Their results are an important step towards demonstrating the feasibility of using MeerKAT and SKA-Mid in the future to measure the HI distribution and pioneer a novel way to map and explore the Universe on cosmological scales. Similarly, SKA-Low may eventually be used to perform an intensity mapping survey, which would provide unique information about how galaxies form and evolve.

By Jingying Wang (University of the Western Cape) for the Meerklass Team