Four previously unknown galaxy clusters – each potentially containing
thousands of individual galaxies – have been discovered some 10 billion
light years from Earth.
An international team of astronomers, led by
Imperial College London, used a new way of combining data from the two
European Space Agency satellites,
Planck and
Herschel,
to identify more distant galaxy clusters than has previously been
possible. The researchers believe up to 2000 further clusters could be
identified using this technique, helping to build a more detailed
timeline of how clusters are formed. They publish their work in a paper
in the journal
Monthly Notices of the Royal Astronomical Society.
An
artist's impression of the Herschel spacecraft. Credit: ESA/ AOES
Medialab / NASA/ESA/STScI. Click for a full-resolution image.Galaxy
clusters are the most massive objects in the universe, containing
hundreds to thousands of galaxies, bound together by gravity. While
astronomers have identified many nearby clusters, they need to go
further back in time to understand how these structures are formed. This
means finding clusters at greater distances from the Earth.
The light from the most distant of the four new clusters identified
by the team has taken over 10 billion years to reach us. This means the
researchers are seeing what the cluster looked like when the universe
was just three billion years old.
Lead researcher Dr David Clements, from the Department of Physics at
Imperial College London, explains: “Although we’re able to see
individual galaxies that go further back in time, up to now, the most
distant clusters found by astronomers date back to when the universe was
4.5 billion years old. This equates to around nine billion light years
away. Our new approach has already found a cluster in existence much
earlier than that, and we believe it has the potential to go even
further.”
The clusters can be identified at such distances because they contain
galaxies in which huge amounts of dust and gas are being formed into
stars. This process emits light that can be picked up by the satellite
surveys.
Galaxies are divided into two types: elliptical galaxies that have
many stars, but little dust and gas; and spiral galaxies like our own,
the Milky Way, which contain lots of dust and gas. Most clusters in the
universe today are dominated by giant elliptical galaxies in which the
dust and gas has already been formed into stars.
“What we believe we are seeing in these distant clusters are giant
elliptical galaxies in the process of being formed,” says Dr Clements.
Three (false) colour Herschel images of the clumps identified by Planck.
Blue, green and red represent infrared light at successively longer
wavelengths, of 250μm, 350μm and 500μm respectively. The green circle
indicates the size of the Planck beam at the position of the source, which Herschel was able to resolve in far greater detail. Credit: D. Clements / ESA / NASA. Click for a full-resolution image.Observations were recorded by the Spectral and Photometric Imaging Receiver (SPIRE) instrument as part of the
Herschel Multi-tiered Extragalactic Survey (HerMES). Prof Seb Oliver, Head of the HerMES survey said: "The fantastic thing about
Herschel-SPIRE
is that we are able to scan very large areas of the sky with sufficient
sensitivity and image sharpness that we can find these rare and exotic
things. This result from Dr Clements is exactly the kind of thing we
were hoping to find with the HerMES survey".
The researchers are among the first to combine data from two satellites that ended their operations last year: the
Planck satellite, which scanned the whole sky, and the
Herschel satellite, which surveyed certain sections in greater detail. The researchers used
Planck data to find sources of far-infrared emission in areas covered by the
Herschel satellite, then cross referenced with
Herschel
data to look at these sources more closely. Of sixteen sources
identified by the researchers, most were confirmed as single, nearby
galaxies that were already known. However, four were shown by
Herschel to be formed of multiple, fainter sources, indicating previously unknown galaxy clusters.
The team then used additional existing data and new observations to
estimate the distance of these clusters from Earth and to determine
which of the galaxies within them were forming stars. The researchers
are now looking to identify more galaxy clusters using this technique,
with the aim of looking further back in time to the earliest stage of
cluster formation.
The research involved scientists from the UK, Spain, USA, Canada, Italy and South Africa. It was part funded by the
Science and Technology Facilities Research Council and the
UK Space Agency.
http://www.ras.org.uk/news-and-press/news-archive/254-news-2014/2396-four-new-galaxy-clusters-take-researchers-further-back-in-time