Astronomers release first part of deep all-sky radio survey with LOFAR
A major new radio sky survey has revealed hundreds of thousands of previously undetected galaxies, shedding new light on many research areas including the physics of black holes and how clusters of galaxies evolve.
An international team of more than 200 astronomers from 18 countries, in which Edinburgh astronomers play a leading role, has published the first phase of the survey at unprecedented sensitivity using the Low Frequency Array (LOFAR) telescope.
Radio astronomy reveals processes in the Universe that we cannot see with optical instruments. In this first part of the sky survey, LOFAR observed a quarter of the northern hemisphere at low radio frequencies. Around ten percent of that data has been made public; a special issue of the scientific journal Astronomy & Astrophysics is dedicated to the first 26 research papers describing the survey and its first results. This first data release maps three hundred thousand sources, almost all of which are galaxies in the distant Universe; their radio signals have travelled billions of light years before reaching Earth.
When we look up at the sky with a radio telescope we see mainly emission from the immediate environment of massive black holes. Professor Philip Best (School of Physics and Astronomy, and PI of the LOFAR-UK consortium) explained:
What we do know is that black holes are pretty messy eaters. When gas falls onto them they emit jets of material that can be seen at radio wavelengths. LOFAR has a remarkable sensitivity which allows us to study black holes even in galaxies which only have jets on very small scales.
Dr Jose Sabater, who works in Best’s research group, has used the new LOFAR data to discover that these jets are present in all of the most massive galaxies.
Prof Philip Best explains:
This means that their black holes never stop eating. The energy output in these radio jets plays a crucial role in controlling the conversion of gas into stars in their surrounding galaxies.
Processing data to produce images
LOFAR produces enormous amounts of data. The equivalent of ten million DVDs of data has been processed to create the low-frequency radio sky map. The survey was made possible by a mathematical breakthrough in the way we understand interferometry. A large international team has been working to efficiently transform the massive amounts of data into high-quality images. Pre-processing of the LOFAR data within the archives in the Netherlands, Germany and Poland reduces the size of the huge LOFAR datasets before the data are transported to member institutions for the images to be made. Most of the images for the first data release were made on the LOFAR-UK high-performance computing facility located at the University of Hertfordshire.
Prof Philip Best reported:
Making these images in a completely automated way has required many years of software development, as well as investment in advanced computer hardware but it’s all been worthwhile for the unprecedented quality of the images, which are allowing us to study the evolution of galaxies and their activity in more detail than ever before.
The LOFAR telescope is unique in its capabilities to map the sky in fine detail at metre wavelengths and is considered to be the world’s leading telescope of its type. The European network of radio antennas spans seven countries and includes the UK station at STFC RAL Space’s Chilbolton Observatory in Hampshire. LOFAR was designed, built, and is now operated by ASTRON in The Netherlands. The signals from all of the stations are combined to make the radio images. This effectively gives astronomers a much larger telescope than it is practical to build - and the bigger the telescope, the better the resolution. The first phase of the survey only processed data from the central stations located in the Netherlands, but UK astronomers are now re-processing the data with all of the international stations to provide resolution twenty times better.
The UK contribution to LOFAR is funded by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).