The South African Radio Astronomy Observatory’s (SARAO’s) MeerKAT radio telescope array has delivered another important radio astronomy first. It has successfully imaged faint, Milky Way-type radio galaxies at distances of between 8-billion and 11-billion light years from Earth. MeerKAT is composed of 64 dish antennas.
“To make this image, we selected an area in the Southern Sky that contains no strong radio sources whose glare could blind a sensitive observation,” reported SARAO researcher Tom Mauch. That area was then observed for 130 hours to capture the image, which has been named DEEP2. (Mauch led the international team of astronomers who were responsible for obtaining and are analysing the image.)
The team’s results have been published in The Astrophysical Journal. The aim of the observations was to increase our knowledge about star formation in the universe. Stars have been forming for the past 13-billion years, but most stars were formed, or born, in a period known as cosmic noon, which was 8-billion to 11-billion years ago.
However, observing star formation during this period has hitherto proven difficult. While optical telescopes can see deep into the cosmos, they cannot see through clouds of dust and gas, and most new stars are hidden inside such clouds. Radio telescopes can see through such clouds, but, until now, have lacked the sensitivity to detect new stars forming in the faint galaxies, which are similar to our own galaxy, the Milky Way, and are where most star formation takes place.
“Because radio waves travel at the speed of light, this [DEEP2] image is a time machine that samples star formation in these distant galaxies over billions of years,” pointed out US National Radio Astronomy Observatory researcher and paper coauthor James Condon. “Because only short-lived stars that are less than 30-million years old send out radio waves, we know that the image is not contaminated by old stars. The radio light we see from each galaxy is therefore proportional to its star-forming rate at that moment in time.”
“These first results indicate that the star-formation rate around cosmic noon is even higher than was originally expected,” stated (US) University of Virginia PhD student Allison Matthews. “Previous images could only detect the tip of the iceberg, the rare and luminous galaxies that produced only a small fraction of the stars in the universe. What we see now is the complete picture: these faint dots [in the image] are the galaxies that formed most of the stars in the universe.”
“MeerKAT is the best radio array in the world for studies like this one because it is the first to use such a large number of extremely low-noise clear-aperture dishes,” noted SARAO chief technologist Justin Jonas. This is why it was able to capture an image of these remote star-forming galaxies that was more sensitive that any previous image. MeerKAT, inaugurated in 2018, is in fact the world’s most sensitive radio telescope of its type. Located in the Karoo region of the Northern Cape province, its 64 dishes are spread over a diameter of 8 km. It is also a precursor for the international Square Kilometre Array (SKA) radio telescope, the core elements of which will be cohosted by South Africa and Australia.
SARAO manages all radio astronomy facilities and programmes in South Africa and is responsible for South Africa’s involvement in, and contribution to, the SKA. In addition to MeerKAT, the Hartebeesthoek Radio Astronomy Observatory, west of Pretoria, falls under SARAO. The South African institution also coordinates the African Very Long Baseline Interferometry Network.