Page 30 - EngineerIt April 2021

SPACE SCIENCES

Ultra-sensitive radio images reveal

thousands of star-forming galaxies

in early Universe

An international team of astronomers has published the most sensitive images of the Universe ever
taken at low radio frequencies, using the International Low Frequency Array (LOFAR).

he software needed to do this, specifically that which “The combination of the high sensitivity of LOFAR and the
handles the direction-dependent effects that would wide area of sky covered by our survey – about 300 times
Totherwise contaminate the images, goes back to the the size of the full moon – has enabled us to detect tens of
work of a former Rhodes University Postdoc Dr Cyril Tasse, thousands of galaxies like the Milky Way, far out into the distant
who remains an honorary research associate of the university, Universe. The light from these galaxies has been travelling for
and Prof. Oleg Smirnov, SKA (Square Kilometre Array) chair billions of years to reach the Earth; this means that we see the
in Radio Astronomy Techniques and Technologies at Rhodes galaxies as they were billions of years ago, back when they
University and head of the Radio Astronomy Research Group were forming most of their stars.”
at SARAO.
By observing the same regions of sky over and over again
and combining the data to make a single, very long exposure
image, the international team has detected the faint radio glow
of stars exploding as supernovae, in tens of thousands of
galaxies, out to the most distant parts of the Universe. A special
issue of the scientific journal Astronomy & Astrophysics is
dedicated to 14 research papers describing these images and
the first scientific results.
“At LOFAR frequencies, observing the sky is like lying on
the bottom of a swimming pool looking up, trying to make out
patterns on the ceiling through the choppy water (the “water”
being the ionosphere). Some very clever software was required
to achieve this,” said Prof. Smirnov.
A collaboration between the two academics led to a paper
describing the maths (Smirnov & Tasse 2015, MNRAS), and
to the DDFacet/killMS software packages that Dr Tasse had
helped develop over the years. These packages are now at the
heart of LOFAR data processing.
“We quickly realised the same software can also be used to
make MeerKAT images better, and several young researchers
from Rhodes University and SARAO also became involved in
this project with Dr Tasse,” explained Prof. Smirnov.
Prof. Philip Best from the University of Edinburgh, UK, who The image shows the deepest LOFAR image ever made, in the
led the deep survey, said: “When we look at the sky with a region of sky known as ‘Elais-N1’, which is one of the three fields
studied as part of this deep radio survey. The image arises from
radio telescope, the brightest objects we see are produced by a single LOFAR pointing observed repeatedly for a total of 164
massive black holes at the centre of galaxies. However, our hours. Over 80,000 radio sources are detected; this includes
images are so deep that most of the objects in it are galaxies some spectacular large-scale emission arising from massive
like our own Milky Way, which emit faint radio waves that trace black holes, but most sources are distant galaxies like the Milky
their ongoing star formation.” Way, forming their stars.

EngineerIT | April 2021 | 28