February 12, 2014
Planck And Herschel Help Identify Four New Distant Galaxy Clusters
Brett Smith for redOrbit.com - Your Universe Online
Using a novel way of combining data from the two European Space Agency (ESA) satellites Planck and Herschel, an international team of scientists has been able to locate more distant galaxy clusters than previously possible.
According to the team’s report in the Monthly Notices of the Royal Astronomical Society, they were able to use their new technique to discover four previously unknown galaxy clusters containing thousands of individual galaxies located 10 billion light years from Earth.
Galaxy clusters are the biggest astronomical objects in the universe, each one consisting of hundreds to thousands of galaxies – all held together by gravity. To understand how these groupings are formed, astronomers need to find clusters located great distances from Earth – essentially peeking back in time since the light from them takes millions of years to reach us.
While scientists have found many clusters close to Earth, they have yet to find significant numbers of these distant clusters. The study team speculated that their new technique could lead to 2,000 additional clusters being identified.
"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,” said study author David Clements, from the Department of Physics at Imperial College London. “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."
Galaxy clusters can be identified by satellite surveys at such great distances because they contain galaxies involving tremendous amounts of dust and gas that are being molded into stars, a process that emits significant amounts of detectable light. However, most galaxy clusters in the modern universe are covered with giant elliptical galaxies in which the dust and gas has previously been made into stars.
"What we believe we are seeing in these distant clusters are giant elliptical galaxies in the process of being formed," Clements said.
Data used in the study was taken from the Spectral and Photometric Imaging Receiver (SPIRE) instrument as part of the ESA’s Herschel Multi-tiered Extragalactic Survey (HerMES).
"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,” said Seb Oliver, who leads the HerMES survey team. “This result from Dr. Clements is exactly the kind of thing we were hoping to find with the HerMES survey."
The study team has used Planck data to find sources of far-infrared emission in areas covered by the Herschel satellite. The Planck data was then cross-referenced with Herschel data to examine these emissions sources more closely. Of the 16 sources identified by the scientists, most were found to be single, close-by galaxies that were already known. However, four were shown by Herschel to be multiple, fainter sources, an indication of earlier unknown galaxy clusters.
The study researchers also used a combination of existing data and new observations to determine the distance of these clusters from Earth and to figure out which of the galaxies were star-forming. The team said they are now trying to find more galaxy clusters using this novel technique.
Image 2 (below): Three (false) color 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