Wednesday, 20 August 2014

Most Massive Known Galaxies Observed at Edge of the Universe (Today's Most Popular)


Four previously unknown galaxy clusters each potentially containing thousands of individual galaxies have been discovered some 10 billion light years from Earth. 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 David Clements, from the Department of Physics at Imperial College London.

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.
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.

"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," explains Clements. "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.

Observations were recorded by the Spectral and Photometric Imaging Receiver (SPIRE) instrument as part of Herschel Multi-tiered Extragalactic Survey (HerMES). 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.

NGC 7049 shown at the top of the page is a giant galaxy on the border between spiral and elliptical galaxies that spans about 150,000 light-years. It is located about 100 million light-years away from Earth in the southern constellation of Indus. NGC 7049 is the “brightest” galaxy of the Indus Triplet of galaxies (NGC 7029, NGC 7041, NGC 7049), and its structure might have arisen from several recent galaxy collisions.

Bright Cluster Galaxies are among the most massive galaxies in the universe and are also the oldest. They provide astronomers the opportunity of studying the many globular clusters contained within them. NGC 7049 has far fewer such clusters than other similar giant galaxies in very big, rich groups. This indicates to astronomers how the surrounding environment influenced the formation of galaxy halos in the early Universe.

The globular clusters in NGC 7049 are seen as the sprinkling of small faint points of light in the galaxy’s halo. The halo – the ghostly region of diffuse light surrounding the galaxy – is composed of myriads of individual stars and provides a luminous background to the remarkable swirling ring of dust lanes surrounding NGC 7049′s core.

NGC 7049′s striking appearance is primarily due to this unusually prominent dust ring, seen mostly in silhouette. The opaque ring is much darker than the millions of bright stars glowing behind it. Generally these dust lanes are seen in much younger galaxies with active star forming regions. Not visible in this image is an unusual central polar ring of gas circling out of the plane near the galaxy’s center.

The image was taken by the Advanced Camera for Surveys on the Hubble Space Telescope, which is optimised to hunt for galaxies and galaxy clusters in the remote and ancient Universe, at a time when our cosmos was very young.

The research involved scientists from the UK, Spain, USA, Canada, Italy and South Africa. It was published in the Monthly Notices of the Royal Astronomical Society and was part funded by the Science and Technology Facilities Research Council and the UK Space Agency.

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