MeerKAT Science – the Large Survey Projects

Article republished with kind permission from SKA Africa.

Professor Roy Booth, SKA South Africa Project

The first science that the MeerKAT will do is encompassed by the large survey projects which were approved by an international Time Allocation Committee in 2010. Five years of observing time have already been allocated to these projects. They cover a wide range of astrophysics, from the evolution of galaxies after their formation in the early universe to nearby exotic objects like pulsating radio sources, neutron stars and even complex molecules in the interstellar medium of our galaxy. The two top priority projects are a deep survey of neutral hydrogen and a pulsar timing survey.

The MeerKAT Large Survey Proposal Review Committee, with SKA Project hosts (fltr) Bernie Fanaroff (South African SKA Project); Roy Maartens (University of the Western Cape); Andrew Lyne (Jodrell Bank); Joseph Lazio (Jet Propulsion Laboratory) (Chair); Frank Briggs (Australian National University, Mount Stromlo Observatory); Roy Booth (SA SKA Project), Simon Johnston (Australia Telescope National Facility); Jay Lockman (National Radio Astronomy Observatory), Athol Kembal (University of Illinois), Robert Laing (European Southern Observatory), Thijs van der Hulst (University of Groningen), Justin Jonas (SA SKA Project).

The excitation of the hydrogen gas formed as the universe cooled after the Big Bang gives the spectroscopic signature which several of the projects will use to make the deepest studies of the earliest (high red-shift) galaxies. Atomic hydrogen (HI) will be used in the ultra-deep Laduma survey, which is expected to detect the HI content of galaxies from the present time back to when the universe was less than half its current age. The Mesmer survey will search for molecular hydrogen through its surrogate, carbon monoxide (which is easier to detect). Spectral lines of CO will be used to detect denser gas in galactic centres and star-forming clouds. The Doppler effect in the expanding universe shifts the wavelengths of these spectral lines to longer wavelengths and their red-shift, z, gives a measure of the look-back time to the galaxy from which they come.

The atomic hydrogen line is used in several other extragalactic studies:

  • the MeerKAT Absorption Line Survey will detect HI lines and even hydroxyl (OH) in absorption against the continuum emission of distant galaxies
  • a hydrogen survey of the Fornax cluster will study the assembly of clusters, the effect of clustering on galaxies (tidal effects and stripping of gas from galaxies as they fall into the cluster)
  • the Mhongoose survey of nearby galaxies will make very sensitive measurements of galaxies and their environments, and may have the potential to detect the cosmic web, the filamentary structure or ‘skeleton’ of the universe along which the galaxies are believed to form.

Experience shows that when there is a significant improvement in sensitivity in a radio telescope, there is a good chance of detecting new kinds of galaxies. The Mightee survey is a deep survey of continuum emission and polarisation which exploits MeerKAT’s sensitivity to the full with this hope in mind, as well as making more detailed studies of faint objects and making a comparison of their properties from multi-wavelength studies.

MeerGal is a high frequency survey of our own Milky Way galaxy. MeerGal will exploit the upper frequency band of MeerKAT in a survey of the interstellar medium of our galaxy for ionized hydrogen/star formation regions, cold molecular clouds, complex molecules, masers and other interstellar matter. The wide-band receivers of MeerKAT will be ideal for such studies. MeerGal will even cover the investigation of a potential new radio emission mechanism due to spinning dust.

There are two major projects which will investigate the exotic pulsating radio sources, pulsars. The first, and one of the two highest rated projects among the large survey proposals, concentrates on Pulsar Timing, partly in the hope of detecting changes in pulsar periods caused by gravitational waves in order to investigate theories of gravity. MeerKAT’s high frequency band facilitates observations through the ionized medium towards the Galactic Centre – a probable source of gravitational waves. The second pulsar study, Trapum, is a search for new types of pulsars and fast transient sources, some of which have been shown to behave like pulsars for short intervals of time but ‘switch off’ for long periods, without detectable emission. These enigmatic sources remain a puzzle.

Finally, slow (several seconds) transients are the topic of the Thunderkat project. The team expect to detect and study radio emission associated with high-energy gamma ray bursts, radio supernovae and other types of explosive event, in both the nearby and the more distant Universe.

All three of the timing/transient projects are data-hungry and want to sample all data streams from all other projects. Although this will be a headache for our engineers, these surveys hold out a serious promise of very exciting results.

All of the project teams are beginning to ramp up for a meeting of principal investigators in mid-April 2011 in Cape Town, when an exchange of ideas with our MeerKAT engineers will help to refine the MeerKAT systems. We will call for input by the survey teams, especially on aspects of MeerKAT software and the organisation of the data products. Some teams have offered special hardware and are very experienced in organisation and even pre-processing of the data in the pipeline output. Their input will help to ensure efficient data processing across the MeerKAT science projects.