NASA's Hubble Spots Rare Gravitational Arc from Distant, Hefty Galaxy Cluster

IDCS J1426.5+3508

Credit: NASA, ESA, and A. Gonzalez (University of Florida, Gainesville), A. Stanford (University of California, Davis and Lawrence Livermore National Laboratory), and M. Brodwin (University of Missouri-Kansas City and Harvard-Smithsonian Center for Astrophysics)

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Seeing is believing, except when you don't believe what you see.

Astronomers using NASA's Hubble Space Telescope have found a puzzling arc of light behind an extremely massive cluster of galaxies residing 10 billion light-years away. The galactic grouping, discovered by NASA's Spitzer Space Telescope, was observed when the universe was roughly a quarter of its current age of 13.7 billion years. The giant arc is the stretched shape of a more distant galaxy whose light is distorted by the monster cluster's powerful gravity, an effect called gravitational lensing.

The trouble is, the arc shouldn't exist.

"When I first saw it, I kept staring at it, thinking it would go away," said study leader Anthony Gonzalez of the University of Florida in Gainesville. "According to a statistical analysis, arcs should be extremely rare at that distance. At that early epoch, the expectation is that there are not enough galaxies behind the cluster bright enough to be seen, even if they were 'lensed' or distorted by the cluster. The other problem is that galaxy clusters become less massive the farther back in time you go. So it's more difficult to find a cluster with enough mass to be a good lens for gravitationally bending the light from a distant galaxy."

Galaxy clusters are collections of hundreds to thousands of galaxies bound together by gravity. They are the most massive structures in our universe. Astronomers frequently study galaxy clusters to look for faraway, magnified galaxies behind them that would otherwise be too dim to see with telescopes. Many such gravitationally lensed galaxies have been found behind galaxy clusters closer to Earth.

The surprise in this Hubble observation is spotting a galaxy lensed by an extremely distant cluster. Dubbed IDCS J1426.5+3508, the cluster is the most massive found at that epoch, weighing as much as 500 trillion suns. It is 5 to 10 times larger than other clusters found at such an early time in the universe's history. The team spotted the cluster in a search using NASA's Spitzer Space Telescope in combination with archival optical images taken as part of the National Optical Astronomy Observatory's Deep Wide Field Survey at the Kitt Peak National Observatory, Tucson, Ariz. The combined images allowed them to see the cluster as a grouping of very red galaxies, indicating they are far away.

This unique system constitutes the most distant cluster known to "host" a giant gravitationally lensed arc. Finding this ancient gravitational arc may yield insight into how, during the first moments after the big bang, conditions were set up for the growth of hefty clusters in the early universe.

The arc was spotted in optical images of the cluster taken in 2010 by Hubble's Advanced Camera for Surveys. The infrared capabilities of Hubble's Wide Field Camera 3 (WFC3) helped provide a precise distance, confirming it to be one of the farthest clusters yet discovered.

Once the astronomers determined the cluster's distance, they used Hubble, the Combined Array for Research in Millimeter-wave Astronomy (CARMA) radio telescope, and NASA's Chandra X-ray Observatory to independently show that the galactic grouping is extremely massive.

CARMA helped the astronomers determine the cluster's mass by measuring how primordial light from the big bang was affected as it passed through the extremely hot, tenuous gas that permeates the grouping. The astronomers then used the WFC3 observations to map the cluster's mass by calculating how much cluster mass was needed to produce the gravitational arc. Chandra data, which revealed the cluster's brightness in X-rays, was also used to measure the cluster's mass.

"The chance of finding such a gigantic cluster so early in the universe was less than one percent in the small area we surveyed," said team member Mark Brodwin of the University of Missouri-Kansas City. "It shares an evolutionary path with some of the most massive clusters we see today, including the Coma Cluster and the recently discovered El Gordo Cluster."

An analysis of the arc revealed that the lensed object is a star-forming galaxy that existed 10 billion to 13 billion years ago. The team hopes to use Hubble again to obtain a more accurate distance to the lensed galaxy.

Gonzalez has considered several possible explanations for the arc.

One explanation is that distant galaxy clusters, unlike nearby clusters, have denser concentrations of galaxies at their cores, making them better magnifying glasses. However, even if the distant cores were denser, the added bulk still should not provide enough gravitational muscle to produce the giant arc seen in Gonzalez's observations, according to a statistical analysis.

Another possibility is that the initial microscopic fluctuations in matter made right after the big bang were different from those predicted by standard cosmological simulations, and therefore produced more massive clusters than expected.

"I'm not yet convinced by any of these explanations," Gonzalez said. "After all, we have found only one example. We really need to study more extremely massive galaxy clusters that existed between 8 billion and 10 billion years ago to see how many more gravitationally lensed objects we can find."

The team's results are described in three papers, which will appear online today and will be published in the July 10, 2012, issue of The Astrophysical Journal. Gonzalez is the first author on one of the papers; Brodwin, on another; and Adam Stanford of the University of California at Davis, on the third.

CONTACT

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Anthony Gonzalez
University of Florida, Gainesville, Fla.
352-392-2052 x233
anthony@astro.ufl.edu

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Colliding galaxy cluster unravelled

Galaxy cluster Abell 2256 at 60 MHz made with LOFAR

Click here for a high res image

An international team of astronomers has used the International LOFAR Telescope from ASTRON, the Netherlands Institute for Radio Astronomy, to study the formation of the galaxy cluster Abell 2256. Abell 2256 is a cluster containing hundreds of galaxies at a distance of 800 million lightyears. ‘The structure we see in the radio images made with LOFAR provides us with information about the origin of this cluster, explains lead author dr. Reinout van Weeren (Leiden University and ASTRON). The study will be published in the scientific journal Astronomy & Astrophysics. The research involved a large team of scientists from 26 different universities and research institutes.

LOFAR has made the first images of Abell 2256 in the frequency range of 20 to 60 MHz. What came as a surprise to scientists was that the cluster of galaxies was brighter and more complex than expected. Dr. van Weeren: ‘We think that galaxy clusters form by mergers and collisions of smaller clusters'. Abell 2256 is a prime example of a cluster that is currently undergoing a collision. The radio emission is produced by tiny elementary particles that move nearly at the speed of light. With LOFAR it is possible to study how these particles get accelerated to such speeds. ‘In particular, we will learn how this acceleration takes place in regions measuring more than 10 million light years across', says Dr. Gianfranco Brunetti from IRA-INAF in Bologna, Italy, who together with Prof. Marcus Brüggen from the Jacobs University in Bremen, coordinates the LOFAR work on galaxy clusters.

LOFAR was built by a large international consortium led by the Netherlands and which includes Germany, France, the United Kingdom and Sweden. One of the main goals of LOFAR is to survey the entire northern sky at low radio frequencies, with a sensitivity and resolution about 100 times better than what has been previously done. Scientists believe that this survey will discover more than 100 million objects in the distant Universe. ‘Soon we will start our systematic surveys of the sky that will lead to great discoveries', says Prof. Huub Röttgering from Leiden University and Principal Investigator of the "LOFAR Survey Key Project".


For more information, contact:

Dr. Reinout van Weeren, astronomer,
Leiden University and ASTRON
Tel.: +31 71 527 5864
E-mail: rvweeren@strw.leidenuniv.nl
Prof. Huub Röttgering, astronomer,
Leiden University
Tel.: +31 6 41522603
E-mail: rottgering@strw.leidenuniv.nl

Femke Boekhorst,
PR & Communication, ASTRON
Tel.: +31 521 595 204
E-mail: boekhorst@astron.nl

Link to the paper:
http://home.strw.leidenuniv.nl/~rvweeren/A2256_LBA_arx.pdf

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Herschel Sees Intergalactic Bridge Aglow With Stars

The Herschel Space Observatory has discovered a giant, galaxy-packed filament ablaze with billions of new stars. The filament connects two clusters of galaxies that, along with a third cluster, will smash together in several billion years and give rise to one of the largest galaxy superclusters in the universe. Image credit: ESA/NASA/JPL-Caltech/CXC/McGill Univ. Full image and caption

The Herschel Space Observatory has discovered a giant, galaxy-packed filament ablaze with billions of new stars. The filament connects two clusters of galaxies that, along with a third cluster, will smash together and give rise to one of the largest galaxy superclusters in the universe.

Herschel is a European Space Agency mission with important NASA contributions.

The filament is the first structure of its kind spied in a critical era of cosmic buildup when colossal collections of galaxies called superclusters began to take shape. The glowing galactic bridge offers astronomers a unique opportunity to explore how galaxies evolve and merge to form superclusters.

"We are excited about this filament, because we think the intense star formation we see in its galaxies is related to the consolidation of the surrounding supercluster," says Kristen Coppin, an astrophysicist at McGill University in Canada, and lead author of a new paper in Astrophysical Journal Letters.

"This luminous bridge of star formation gives us a snapshot of how the evolution of cosmic structure on very large scales affects the evolution of the individual galaxies trapped within it," says Jim Geach, a co-author who is also based at McGill.

The intergalactic filament, containing hundreds of galaxies, spans 8 million light-years and links two of the three clusters that make up a supercluster known as RCS2319. This emerging supercluster is an exceptionally rare, distant object whose light has taken more than seven billion years to reach us.

RCS2319 is the subject of a huge observational study, led by Tracy Webb and her group at McGill. Previous observations in visible and X-ray light had found the cluster cores and hinted at the presence of a filament. It was not until astronomers trained Herschel on the region, however, that the intense star-forming activity in the filament became clear. Dust obscures much of the star-formation activity in the early universe, but telescopes like Herschel can detect the infrared glow of this dust as it is heated by nascent stars.

The amount of infrared light suggests that the galaxies in the filament are cranking out the equivalent of about 1,000 solar masses (the mass of our sun) of new stars per year. For comparison's sake, our Milky Way galaxy is producing about one solar-mass worth of new stars per year.

Researchers chalk up the blistering pace of star formation in the filament to the fact that galaxies within it are being crunched into a relatively small cosmic volume under the force of gravity. "A high rate of interactions and mergers between galaxies could be disturbing the galaxies' gas reservoirs, igniting bursts of star formation," said Geach.

By studying the filament, astronomers will be able to explore the fundamental issue of whether "nature" versus "nurture" matters more in the life progression of a galaxy. "Is the evolution of a galaxy dominated by intrinsic properties such as total mass, or do wider-scale cosmic environments largely determine how galaxies grow and change?" Geach asked. "The role of the environment in influencing galactic evolution is one of the key questions of modern astrophysics."

The galaxies in the RCS2319 filament will eventually migrate toward the center of the emerging supercluster. Over the next seven to eight billion years, astronomers think RCS2319 will come to look like gargantuan superclusters in the local universe, like the nearby Coma cluster. These advanced clusters are chock-full of "red and dead" elliptical galaxies that contain aged, reddish stars instead of young ones.

"The galaxies we are seeing as starbursts in RCS2319 are destined to become dead galaxies in the gravitational grip of one of the most massive structures in the universe," said Geach. "We're catching them at the most important stage of their evolution."

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA.

More information is online at http://www.herschel.caltech.edu , http://www.nasa.gov/herschel and http://www.esa.int/SPECIALS/Herschel .

Written by Adam Hadhazy
Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

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Hubble Sees the Eye of the Storm in Galaxy Cluster

Abell 1185

Credit: ESA/Hubble & NASA
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This image from the NASA/ESA Hubble Space Telescope could seem like a quiet patch of sky at first glance. But zooming into the central part of a galaxy cluster — one of the largest structures of the Universe — is rather like looking at the eye of the storm.

Clusters of galaxies are large groups consisting of dozens to hundreds of galaxies, which are bound together by gravity. The galaxies sometimes stray too close to one another and the huge gravitational forces at play can distort them or even rip matter off when they collide with one another.

This particular cluster, called Abell 1185, is a chaotic one. Galaxies of various shapes and sizes are drifting dangerously close to one another. Some have already been ripped apart in this cosmic maelstrom, shedding trails of matter into the void following their close encounter. They have formed a familiar shape called The Guitar, located just outside the frame of this image.

Abell 1185 is located approximately 400 million light-years away from Earth and spans one million light-years across. A few of the elliptical galaxies that form the cluster are visible in the corners of this image, but mostly, the small elliptical shapes seen are faraway galaxies in the background, located much further away, in a quieter area of the Universe.

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DLSCL J0916.2+2951: Discovery of the Musket Ball Cluster

Musket Ball Cluster
Credit X-ray: NASA/CXC/UCDavis/W.Dawson et al;

Optical: NASA/STScI/UCDavis/W.Dawson et al.

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Using a combination of powerful observatories in space and on the ground, astronomers have observed a violent collision between two galaxy clusters in which so-called normal matter has been wrenched apart from dark matter through a violent collision between two galaxy clusters.

The newly discovered galaxy cluster is called DLSCL J0916.2+2951. It is similar to the Bullet Cluster, the first system in which the separation of dark and normal matter was observed, but with some important differences. The newly discovered system has been nicknamed the "Musket Ball Cluster" because the cluster collision is older and slower than the Bullet Cluster.

Finding another system that is further along in its evolution than the Bullet Cluster gives scientists valuable insight into a different phase of how galaxy clusters - the largest known objects held together by gravity - grow and change after major collisions. Researchers used observations from NASA's Chandra X-ray Observatory and Hubble Space Telescope as well as the Keck, Subaru and Kitt Peak Mayall telescopes to show that hot, X-ray bright gas in the Musket Ball Cluster has been clearly separated from dark matter and galaxies.

In this composite image, the hot gas observed with Chandra is colored red, and the galaxies in the optical image from Hubble appear as mostly white and yellow. The location of the majority of the matter in the cluster (dominated by dark matter) is colored blue. When the red and the blue regions overlap, the result is purple as seen in the image. The matter distribution is determined by using data from Subaru, Hubble and the Mayall telescope that reveal the effects of gravitational lensing, an effect predicted by Einstein where large masses can distort the light from distant objects.

In addition to the Bullet Cluster, five other similar examples of merging clusters with separation between normal and dark matter and varying levels of complexity, have previously been found. In these six systems, the collision is estimated to have occurred between 170 million and 250 million years

Bullet Cluster

Credit X-ray: NASA/CXC/CfA/M.Markevitch et al.;

Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.;
Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

In the Musket Ball Cluster, the system is observed about 700 million years after the collision. Taking into account the uncertainties in the age estimate, the merger that has formed the Musket Ball Cluster is two to five times further along than in previously observed systems. Also, the relative speed of the two clusters that collided to form the Musket Ball cluster was lower than most of the other Bullet Cluster-like objects.

The special environment of galaxy clusters, including the effects of frequent collisions with other clusters or groups of galaxies and the presence of large amounts of hot, intergalactic gas, is likely to play an important role in the evolution of their member galaxies. However, it is still unclear whether cluster mergers trigger star formation, suppress it, or have little immediate effect. The Musket Ball Cluster holds promise for deciding between these alternatives.

The Musket Ball Cluster also allows an independent study of whether dark matter can interact with itself. This information is important for narrowing down the type of particle that may be responsible for dark matter. No evidence is reported for self-interaction in the Musket Ball Cluster, consistent with the results for the Bullet Cluster and the other similar clusters.

The Musket Ball Cluster is located about 5.2 billion light years away from Earth. A paper describing these results was led by Will Dawson from University of California, Davis and was published in the March 10, 2012 issue of The Astrophysical Journal Letters. The other co-authors were David Wittman, M. James Jee and Perry Gee from UC Davis, Jack Hughes from Rutgers University in NJ, J. Anthony Tyson, Samuel Schmidt, Paul Thorman and Marusa Bradac from UC Davis, Satoshi Miyazaki from the Graduate University for Advanced Studies (GUAS) in Tokyo, Japan, Brian Lemaux from UC Davis, Yousuke Utsumi from GUAS and Vera Margoniner from California State University, Sacramento.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

Fast Facts for DLSCL J0916.2+2951:

Scale: 6.4 arcmin across (about 8 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 09h 16m 14.64s | Dec +29° 54' 24.00"
Constellation: Cancer
Observation Date: Jan 2, 2011
Observation Time: 11 hours 6 min.
Obs. ID: 12913
Color Code: Optical (Red, Green, Blue); X-ray (Red-Purple); Mass Map (Blue)
Instrument: ACIS
References: Dawson, W. et al, 2012, ApJ 747, 42; arXiv:1110.4391
Distance Estimate: 5.23 billion light years (z=0.53)

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Abell 383: Getting a Full Picture of an Elusive Subject

Abell 383

Credit: X-ray: NASA/CXC/Caltech/A.Newman et al/Tel Aviv/A.Morandi & M.Limousin; Optical: NASA/STScI, ESO/VLT, SDSS

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Two teams of astronomers have used data from NASA's Chandra X-ray Observatory and other telescopes to map the distribution of dark matter in a galaxy cluster known as Abell 383, which is located about 2.3 billion light years from Earth. Not only were the researchers able to find where the dark matter lies in the two dimensions across the sky, they were also able to determine how the dark matter is distributed along the line of sight.

Dark matter is invisible material that does not emit or absorb any type of light, but is detectable through its gravitational effects. Several lines of evidence indicate that there is about six times as much dark matter as "normal", or baryonic, matter in the Universe. Understanding the nature of this mysterious matter is one of the outstanding problems in astrophysics.

Galaxy clusters are the largest gravitationally-bound structures in the universe, and play an important role in research on dark matter and cosmology, the study of the structure and evolution of the universe. The use of clusters as dark matter and cosmological probes hinges on scientists' ability to use objects such as Abell 383 to accurately determine the three-dimensional structures and masses of clusters.

The recent work on Abell 383 provides one of the most detailed 3-D pictures yet taken of dark matter in a galaxy cluster. Both teams have found that the dark matter is stretched out like a gigantic football, rather than being spherical like a basketball, and that the point of the football is aligned close to the line of sight.

The X-ray data (purple) from Chandra in the composite image show the hot gas, which is by far the dominant type of normal matter in the cluster. Galaxies are shown with the optical data from the Hubble Space Telescope (HST), the Very Large Telescope, and the Sloan Digital Sky Survey, colored in blue and white.

Both teams combined the X-ray observations of the "normal matter" in the cluster with gravitational lensing information determined from optical data. Gravitational lensing - an effect predicted by Albert Einstein - causes the material in the galaxy cluster, both normal and dark matter, to bend and distort the optical light from background galaxies. The distortion is severe in some parts of the image, producing an arc-like appearance for some of the galaxies. In other parts of the image the distortion is subtle and statistical analysis is used to study the distortion effects and probe the dark matter.

A considerable amount of effort has gone into studying the center of galaxy clusters, where the dark matter has the highest concentration and important clues about its behavior might be revealed. Both of the Abell 383 studies reported here continue that effort.

The team of Andrea Morandi from Tel Aviv University in Israel and Marceau Limousin from Université de Provence in France and University of Copenhagen in Denmark concluded that the increased concentration of the dark matter toward the center of the cluster is in agreement with most theoretical simulations. Their lensing data came from HST images.

The team led by Andrew Newman of the California Institute of Technology and Tommaso Treu of University of California, Santa Barbara (UCSB) used lensing data from HST and the Japanese telescope Subaru, but added Keck observations to measure the velocities of stars in the galaxy in the center of the cluster, allowing for a direct estimate of the amount of matter there. They found evidence that the amount of dark matter is not peaked as dramatically toward the center as the standard cold dark matter model predicts. Their paper describes this as being the "most robust case yet" made for such a discrepancy with the theory.

The contrasting conclusions reached by the two teams most likely stem from differences in the data sets and the detailed mathematical modeling used. One important difference is that because the Newman et al. team used velocity information in the central galaxy, they were able to estimate the density of dark matter at distances that approached as close as only 6,500 light years from the center of the cluster. Morandi and Limousin did not use velocity data and their density estimates were unable to approach as close to the cluster's center, reaching to within 80,000 light years.

Another important difference is that Morandi and Limousin used a more detailed model for the 3-D map of dark matter in the cluster. For example, they were able to estimate the orientation of the dark matter "football" in space and show that it is mostly edge-on, although slightly tilted with respect to the line of sight.

As is often the case with cutting-edge and complex results, further work will be needed to resolve the discrepancy between the two teams. In view of the importance of resolving the dark matter mystery, there will undoubtedly be much more research into Abell 383 and other objects like it in the months and years to come.

If the relative lack of dark matter in the center of Abell 383 is confirmed, it may show that improvements need to be made in our understanding of how normal matter behaves in the center of galaxy clusters, or it may show that dark matter particles can interact with each other, contrary to the prevailing model.

The Newman et al. paper was published in the February 20, 2011 issue of the Astrophysical Journal Letter and the Morandi and Limousin paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society. Other members of the Newman et al. team were Richard Ellis from Caltech, and David Sand from Las Cumbres Global Telescope Network and UCSB.

Fast Facts for Abell 383:

Scale: 7.26 arcmin across (4.84 million light years)
Category: Groups & Clusters of Galaxies
Coordinates: (J2000) RA 02h 48m 06.96s | Dec -03º 29' 31.81"
Constellation: Eridanus
Observation Date: 3 pointings between Sep and Nov 2000
Observation Time: 13 hours 43 min.
Obs. ID: 524, 2320, 2321
Color Code: X-ray (Purple), Optical (White & Blue)
Instrument: ACIS

References: Newman,A. et al. 2011 ApJ 728:L39; arXiv:1101.3553; Morandi, A., Limousin, M. 2011 MNRAS (in press);arXiv:1108.0769

Distance Estimate: 2.3 billion light years (z=0.189)

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Riding the Wake of a Merging Galaxy Cluster

Observations using the OASIS integral field spectrograph on the William Herschel Telescope (WHT) have revealed a long, thin plume of ionised gas stretching out from the brightest cluster galaxy (BCG) of Abell 2146 (z=0.243) (Canning et al. 2012). Extended optical emission-line nebulae are not uncommon in the cores of clusters, but the discovery of this particular structure is unexpected, as the host cluster is in the throes of a major merger event (Russell et al. 2010).

How can a >15kpc long plume survive in the environment of such a turbulent intracluster medium? Chandra X-ray observations of the system show that a merging subcluster has created large shock fronts, each several hundred kiloparsecs across. These surround a dense, relatively cool X-ray core which is being stripped of its material in the collision.

An optical image of the merging cluster Abell 2146 taken with the Subaru telescope. The morphology of the hot X-ray gas is shown as blue contours with the dense X-ray cool core unusually leading the brightest cluster galaxy. The majority of cluster galaxies are ahead of the X-ray gas, as expected in a galaxy cluster merger. The positions of the X-ray shock fronts are shown by the red lines. [ PNG | TIFF ]

A peak of cool, dense X-ray gas is usually observed to coincide with the position of the dominant central galaxy in relaxed galaxy clusters. As it has a short radiative cooling time, material condensing out of the hot atmosphere is in a position to contribute to the growth of the dominant galaxy. In a merging cluster core, however, the situation is very different. During a collision between two clusters, individual galaxies can be regarded as effectively collisionless particles. Along with the dark matter component of the clusters, the galaxies thus lead the baryonic gas, which is slowed by friction after the main collision event. The centroids of the dark matter distribution (observationally traced by the galaxies) thus separates from the main baryonic mass component traced by the hot X-ray gas. Observations of this offset in the 'Bullet' cluster merger have provided some of the strongest evidence for dark matter.

The situation in A2146 is unusual. While many of the member galaxies of the merging subcluster are located ahead of the X-ray peak, the dominant cluster galaxy lags behind. A large offset of 36 kpc is observed between the brightest cluster galaxy and the X-ray cool core. The new OASIS observations reveal a thin plume of ionised gas stretching out from the brightest cluster galaxy to bridge the gap to the X-ray cool core. The shape of the plume is tracked by a tail of cooler X-ray gas, linking the dense X-ray peak to the brightest cluster galaxy. This also means that the optical plume could trace an intermediate stage of gas cooling directly from the hot phase and on to the BCG from the X-ray cool core. Whether or not such a process results in significant star formation - thus contributing to the growth of the massive central galaxy - awaits further observation.

A smoothed Chandra X-ray image of Abell 2146 showing the full gas structure. The insert shows the zoomed in image of the X-ray cool core and the brighest cluster galaxy. Low temperature X-ray gas is stripped from the core and coincides with a thin plume of ionised gas extending onto the galaxy. The plume is likely longer than observed and is truncated by the OASIS field-of-view. The colour of the ionised gas shows it's line-of-sight velocity in km per second; smooth low-velocities are observed in the plume while significant rotaion appears to be ongoing in the core of the galaxy. [ PNG | TIFF ]

References:

R. E. A. Canning, H. R. Russell, N. A. Hatch, A. C. Fabian, A. I. Zabludoff, C. S. Crawford, L. J. King, B. R. McNamara, S. Okamoto and S. I. Raimundo, 2012, "Riding the wake of a merging galaxy cluster", MNRAS, 420, DOI : 10.1111/j.1365-2966.2011.20116.x.
Russell H. R., Sanders J. S., Fabian A. C., Baum S. A., Donahue M., Edge A. C., McNamara B. R., O’Dea C. P., 2010, MNRAS, 406, 1721.

Javier Méndez
Public Relations Officer

Source: The Isaac Newton Group of Telescopes (ING)

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Galaxies Get Up Close and Personal

PR Image eso1211a
VST image of the Hercules galaxy cluster

PR Image eso1211b
Highlights of the VST image of the Hercules galaxy cluster

PR Image eso1211c
The location of the Hercules galaxy cluster

PR Image eso1211d
Wide-field view of the Hercules galaxy cluster

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PR Video eso1211a
Zooming in on the Hercules galaxy cluster

PR Video eso1211b
Panning across on the Hercules galaxy cluster

VST captures collisions in young galaxy cluster

The VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile has imaged a fascinating collection of interacting galaxies in the Hercules galaxy cluster. The sharpness of the new picture, and the hundreds of galaxies captured in great detail in less than three hours of observations, attest to the great power of the VST and its huge camera OmegaCAM to explore the nearby Universe.

The Hercules galaxy cluster (also known as Abell 2151) lies about 500 million light-years away in the constellation of Hercules. It is unlike other nearby galactic assemblies in many ways. As well as being rather irregular in shape, it contains a wide variety of galaxy types, particularly young, star-forming spiral galaxies, and there are no giant elliptical galaxies in sight.

The new image was taken with the VST, the most recent addition to ESO’s Paranal Observatory in Chile (eso1119). The VST is a survey telescope equipped with OmegaCAM, a 268-megapixel camera that provides images covering very large areas on the sky. Normally only small telescopes can image large objects such as this in a single shot, but the 2.6-metre VST not only has a wide field, but can also exploit the superb conditions on Paranal to simultaneously obtain very sharp and deep images quickly.

Galaxy pairs getting up close and personal and on their way to merging into single, larger galaxies can be seen all over this image. The numerous interactions, and the large number of gas-rich, star-forming spiral galaxies in the cluster, make the members of the Hercules cluster look like the young galaxies of the more distant Universe [1]. Because of this similarity, astronomers believe that the Hercules galaxy cluster is a relatively young cluster. It is a vibrant and dynamic swarm of galaxies that will one day mature into one more similar to the older galaxy clusters that are more typical of our galactic neighbourhood.

Galaxy clusters are formed when smaller groups of galaxies come together due to the pull of their gravity. As these groups get closer to each other, the cluster becomes more compact and more spherical in shape. At the same time, the galaxies themselves get closer together and many start to interact. Even if spiral galaxies are dominant in the initial groups, the galactic collisions eventually distort their spiral structure and strip off their gas and dust, quenching most star formation. For this reason, most of the galaxies in a mature cluster are elliptical or irregular in shape. One or two large elliptical galaxies, formed from the merger of smaller galaxies and permeated by old stars, usually reside at the centres of these old clusters.

The Hercules galaxy cluster is believed to be a collection of at least three small clusters and groups of galaxies that are currently being assembled into a larger structure. Furthermore, the cluster itself is merging with other large clusters to form a galaxy supercluster. These giant collections of clusters are some of the largest structures in the Universe. The wide field of view and image quality of OmegaCAM on the VST make it ideal for studying the outskirts of galaxy clusters where the poorly-understood interactions between clusters are taking place.

This beautiful image shows not only the galaxies of the Hercules galaxy cluster, but also many faint and fuzzy objects in the background, which are galaxies that are much further away from us. Closer to home, several brilliant Milky Way stars are also visible in the foreground and there are even a few asteroids that have left short trails as they moved slowly across the image during the exposures.

Notes

[1] Objects in the very distant Universe are seen as they were when much younger, because it takes several billion years for their light to reach us.

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The VST programme is a joint venture between the INAF–Osservatorio Astronomico di Capodimonte, Naples, Italy and ESO. INAF designed and built the telescope with the collaboration of leading Italian industries and ESO was responsible for the enclosure and the civil engineering works at the site. OmegaCAM, the VST’s camera, was designed and built by a consortium including institutes in the Netherlands, Germany and Italy with major contributions from ESO. The facility is operated by ESO, which also archives and distributes data from the telescope.

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

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Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

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Dark Matter Core Defies Explanation in Hubble Image

Merging Galaxy Cluster Abell 520
Credit: NASA, ESA, CFHT, CXO, M.J. Jee (University of California, Davis),
and A. Mahdavi (San Francisco State University)
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It was the result no one wanted to believe. Astronomers observed what appeared to be a clump of dark matter left behind during a bizarre wreck between massive clusters of galaxies.

The dark matter collected into a "dark core" containing far fewer galaxies than would be expected if the dark matter and galaxies hung together. Most of the galaxies apparently have sailed far away from the collision. This result could present a challenge to basic theories of dark matter, which predict that galaxies should be anchored to the invisible substance, even during the shock of a collision.

The initial observations, made in 2007, were so unusual that astronomers shrugged them off as unreal, due to poor data. However, new results from NASA's Hubble Space Telescope confirm that dark matter and galaxies parted ways in the gigantic merging galaxy cluster called Abell 520, located 2.4 billion light-years away.

Now, astronomers are left with the challenge of trying to explain dark matter's seemingly oddball behavior in this cluster.

"This result is a puzzle," said astronomer James Jee of the University of California, Davis, leader of the Hubble study. "Dark matter is not behaving as predicted, and it's not obviously clear what is going on. Theories of galaxy formation and dark matter must explain what we are seeing."

A paper reporting the team's results has been accepted for publication in The Astrophysical Journal and is available online.

First detected about 80 years ago, dark matter is thought to be the gravitational "glue" that holds galaxies together. The mysterious invisible substance is not made of the same kind of matter that makes up stars, planets, and people. Astronomers know little about dark matter, yet it accounts for most of the universe's mass.

They have deduced dark matter's existence by observing its ghostly gravitational influence on normal matter. It's like hearing the music but not seeing the band.

One way to study dark matter is by analyzing smashups between galaxy clusters, the largest structures in the universe. When galaxy clusters collide, astronomers expect galaxies to tag along with the dark matter, like a dog on a leash. Clouds of intergalactic gas, however, plow into one another, slow down, and lag behind the impact.

That theory was supported by visible-light and X-ray observations of a colossal collision between two galaxy clusters called the Bullet Cluster. The galactic grouping has become a textbook example of how dark matter should behave.

But studies of Abell 520 showed that dark matter's behavior may not be so simple. The original observations found that the system's core was rich in dark matter and hot gas but contained no luminous galaxies, which normally would be seen in the same location as the dark matter. NASA's Chandra X-ray Observatory detected the hot gas. Astronomers used the Canada-France-Hawaii and Subaru telescopes atop Mauna Kea to infer the location of dark matter by measuring how the mysterious substance bends light from more distant background galaxies, an effect called gravitational lensing.

The astronomers then turned Hubble's Wide Field Planetary Camera 2 to help bail them out of this cosmic conundrum. Instead, to their chagrin, the Hubble observations helped confirm the earlier findings. Astronomers used Hubble to map the dark matter in the cluster through the gravitational lensing technique.

"Observations like those of Abell 520 are humbling in the sense that in spite of all the leaps and bounds in our understanding, every now and then, we are stopped cold," explained Arif Babul of the University of Victoria in British Columbia, the team's senior theorist.

Is Abell 520 an oddball, or is the prevailing picture of dark matter flawed? Jee thinks it's too soon to tell.

"We know of maybe six examples of high-speed galaxy cluster collisions where the dark matter has been mapped," Jee said. "But the Bullet Cluster and Abell 520 are the two that show the clearest evidence of recent mergers, and they are inconsistent with each other. No single theory explains the different behavior of dark matter in those two collisions. We need more examples."

The team has proposed a half-dozen explanations for the findings, but each is unsettling for astronomers. "It's pick your poison," said team member Andisheh Mahdavi of San Francisco State University in California, who led the original Abell 520 observations in 2007. One possible explanation for the discrepancy is that Abell 520 was a more complicated interaction than the Bullet Cluster encounter. Abell 520 may have formed from a collision between three galaxy clusters, instead of just two colliding systems in the case of the Bullet Cluster.

Another scenario is that some dark matter may be what astronomers call "sticky." Like two snowballs smashing together, normal matter slams into each other during a collision and slows down. But dark matter blobs are thought to pass through each other during an encounter without slowing down. This scenario proposes that some dark matter interacts with itself and stays behind when galaxy clusters collide.

A third possibility is that the core contained many galaxies, but they were too dim to be seen, even by Hubble. Those galaxies would have to have formed dramatically fewer stars than other normal galaxies. Armed with the Hubble data, the group hopes to create a computer simulation to try to reconstruct the collision, hoping that it yields some answers to dark matter's weird behavior.

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

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Hubble Zooms in on a Magnified Galaxy

RCS2 032727-132623

Credit: NASA, ESA, J. Rigby (NASA Goddard pace Flight Center), K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago), and M. Gladders and E. Wuyts (University of Chicago). More Images

Thanks to the presence of a natural "zoom lens" in space, NASA's Hubble Space Telescope got a uniquely close-up look at the brightest "magnified" galaxy yet discovered.

This observation provides a unique opportunity to study the physical properties of a galaxy vigorously forming stars when the universe was only one-third its present age.

A so-called gravitational lens is produced when space is warped by a massive foreground object, whether it is the Sun, a black hole, or an entire cluster of galaxies. The light from more-distant background objects is distorted, brightened, and magnified as it passes through this gravitationally disturbed region.

A team of astronomers led by Jane Rigby of NASA's Goddard Space Flight Center in Greenbelt, Md., aimed Hubble at one of the most striking examples of gravitational lensing, a nearly 90-degree arc of light in the galaxy cluster RCS2 032727-132623. Hubble's view of the distant background galaxy is significantly more detailed than could ever be achieved without the help of the gravitational lens.

The results have been accepted for publication in The Astrophysical Journal, in a paper led by Keren Sharon of the Kavli Institute for Cosmological Physics at the University of Chicago. Professor Michael Gladders and graduate student Eva Wuyts of the University of Chicago were also key team members.

The presence of the lens helps show how galaxies evolved from 10 billion years ago to today. While nearby galaxies are fully mature and are at the tail end of their star-formation histories, distant galaxies tell us about the universe's formative years. The light from those early events is just now arriving at Earth. Very distant galaxies are not only faint but also appear small on the sky. Astronomers would like to see how star formation progressed deep within these galaxies. Such details would be beyond the reach of Hubble's vision were it not for the magnification made possible by gravity in the intervening lens region.

In 2006 a team of astronomers using the Very Large Telescope in Chile measured the arc's distance and calculated that the galaxy appears more than three times brighter than previously discovered lensed galaxies. In 2011 astronomers used Hubble to image and analyze the lensed galaxy with the observatory's Wide Field Camera 3.

The distorted image of the galaxy is repeated several times in the foreground lensing cluster, as is typical of gravitational lenses. The challenge for astronomers was to reconstruct what the galaxy really looked like, were it not distorted by the cluster's funhouse-mirror effect.

Hubble's sharp vision allowed astronomers to remove the distortions and reconstruct the galaxy image as it would normally look. The reconstruction revealed regions of star formation glowing like bright Christmas tree bulbs. These are much brighter than any star-formation region in our Milky Way galaxy.

Through spectroscopy, the spreading out of light into its constituent colors, the team plans to analyze these star-forming regions from the inside out to better understand why they are forming so many stars.

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Jane Rigby
NASA Goddard Space Flight Center, Greenbelt, Md.
301-286-1507
jane.r.rigby@nasa.gov

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El Gordo (ACT-CL J0102-4915): NASA's Chandra Finds Largest Galaxy Cluster in Early Universe

Credit X-ray: NASA/CXC/Rutgers/J.Hughes et al, Optical: ESO/VLT/Pontificia Universidad. Catolica de Chile/L.Infante & SOAR (MSU/NOAO/UNC/CNPq-Brazil)/Rutgers/F.Menanteau, IR: NASA/JPL/Rutgers/F.Menanteau

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A composite image shows El Gordo in X-ray light from NASA's Chandra X-ray Observatory in blue, along with optical data from the European Southern Observatory's Very Large Telescope (VLT) in red, green, and blue, and infrared emission from the NASA's Spitzer Space Telescope in red and orange.

X-ray data from Chandra reveal a distinct cometary appearance of El Gordo, including two "tails" extending to the upper right of the image. Along with the VLT's optical data, this shows that El Gordo is, in fact, the site of two galaxy clusters running into one another at several million miles per hour. This and other characteristics make El Gordo akin to the well-known object called the Bullet Cluster, which is located almost 4 billion light years closer to Earth.

As with the Bullet Cluster, there is evidence that normal matter, mainly composed of hot, X-ray bright gas, has been wrenched apart from the dark matter in El Gordo. The hot gas in each cluster was slowed down by the collision, but the dark matter was not.

El Gordo is located over 7 billion light years from Earth, meaning that it is being observed at a young age. According to the scientists involved in this study, this cluster of galaxies is the most massive, the hottest, and gives off the most X-rays of any known cluster at this distance or beyond.

The central galaxy in the middle of El Gordo is unusually bright and has surprisingly blue colors in optical wavelengths. The authors speculate that this extreme galaxy resulted from a collision and merger between the two galaxies at the center of each cluster.

Using Spitzer data and optical imaging it is estimated that about 1% of the total mass of the cluster is in stars, while the rest is found in the hot gas that fills the space between the stars and is detected by Chandra. This ratio of stars to gas is similar with results from other massive clusters.

Fast Facts for El Gordo:

Scale Image is 5.3 arcmin across
Category: Groups & Clusters of Galaxies
Coordinates: (J2000) RA 01h 02m 52.50s | Dec -49° 14' 58.00"
Constellation: Phoenix
Observation Date: 01/26/2011
Observation Time: 16 hours 40 min.
Obs. ID: 12258
Color Code: X-ray (Blue); Optical (Red, Green, Blue); Infrared (Red)
Instrument: ACIS
Also Known As: ACT-CL J0102-4915
References: Menanteau, F. et al, 2011 ApJ (submitted); arXiv:1109.0953
Distance Estimate: 7.166 billion light years

More about → El Gordo (ACT-CL J0102-4915): NASA's Chandra Finds Largest Galaxy Cluster in Early Universe

Abell 2052: A Galaxy Cluster Gets Sloshed

Abell 2052
Credit: X-ray: NASA/CXC/BU/E.Blanton; Optical: ESO/VLT

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Like wine in a glass, vast clouds of hot gas are sloshing back and forth in Abell 2052, a galaxy cluster located about 480 million light years from Earth. X-ray data (blue) from NASA's Chandra X-ray Observatory shows the hot gas in this dynamic system, and optical data (gold) from the Very Large Telescope shows the galaxies. The hot, X-ray bright gas has an average temperature of about 30 million degrees.

A huge spiral structure in the hot gas - spanning almost a million light years - is seen around the outside of the image, surrounding a giant elliptical galaxy at the center. This spiral was created when a small cluster of galaxies smashed into a larger one that surrounds the central elliptical galaxy.

As the smaller cluster approached, the dense hot gas of the central cluster was attracted to it by gravity. After the smaller cluster passed the cluster core, the direction of motion of the cluster gas reversed and it traveled back towards the cluster center. The cluster gas moved through the center again and "sloshed" back and forth, similar to wine sloshing in a glass that was jerked sideways. The sides of the glass push the wine back to the center, whereas in the cluster the gravitational force of the matter in the clusters pulls it back. The sloshing gas ended up in a spiral pattern because the collision between the two clusters was off-center.

Wine sloshing in a glass

Wine sloshing backwards and forwards in a glass provides a small-scale analogy to hot gas sloshing backwards and forwards, over vast scales, in a galaxy cluster. Credit: Markevitch & Vikhlinin (2007)

This type of sloshing in Abell 2052 has important physical implications. First, it helps push some of the more dense, cooler gas located in the center of the cluster -- where temperatures are only about 10 million degrees -- farther away from the core. This helps prevent further cooling of this gas in the core and could limit the amount of new stars being formed in the central galaxy. Sloshing motions like those seen in Abell 2052 also redistribute heavy elements, like iron and oxygen, which are forged in supernova explosions. These elements are used in the future generations of stars and planets and are necessary for life as we know it.

Chandra's observation of Abell 2052 was particularly long, lasting more than a week. Such a deep observation was necessary to detect all of the details in this image. Even then, processing to emphasize more subtle features was necessary to reveal the outer spiral structure.

In addition to the large-scale spiral feature, the deep Chandra observation reveals exquisite detail in the cluster center related to outbursts from the central supermassive black hole. The Chandra data show clear bubbles evacuated by material blasted away from the black hole, which are surrounded by dense, bright, cool rims. As with the sloshing, this activity helps prevent cooling of the gas in the cluster's core, setting limits on the growth of the giant elliptical galaxy and its supermassive black hole.

These results were published in the August 20, 2011 issue of The Astrophysical Journal. The authors were Elizabeth Blanton of Boston University, Boston, MA; Scott Randall of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA; Tracy Clarke of the Naval Research Laboratory in Washington DC; Craig Sarazin of the University of Virginia in Charlottesville, VA; Brian McNamara of the University of Waterloo in Waterloo, Canada; Edmund Douglass of Boston University and Michael McDonald of the University of Maryland, College Park, MD.

This type of sloshing in Abell 2052 has important physical implications. First, it helps push some of the more dense, cooler gas located in the center of the cluster -- where temperatures are only about 10 million degrees -- farther away from the core. This helps prevent further cooling of this gas in the core and could limit the amount of new stars being formed in the central galaxy. Sloshing motions like those seen in Abell 2052 also redistribute heavy elements, like iron and oxygen, which are forged in supernova explosions. These elements are used in the future generations of stars and planets and are necessary for life as we know it.

Chandra's observation of Abell 2052 was particularly long, lasting more than a week. Such a deep observation was necessary to detect all of the details in this image. Even then, processing to emphasize more subtle features was necessary to reveal the outer spiral structure.

In addition to the large-scale spiral feature, the deep Chandra observation reveals exquisite detail in the cluster center related to outbursts from the central supermassive black hole. The Chandra data show clear bubbles evacuated by material blasted away from the black hole, which are surrounded by dense, bright, cool rims. As with the sloshing, this activity helps prevent cooling of the gas in the cluster's core, setting limits on the growth of the giant elliptical galaxy and its supermassive black hole.

These results were published in the August 20, 2011 issue of The Astrophysical Journal. The authors were Elizabeth Blanton of Boston University, Boston, MA; Scott Randall of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA; Tracy Clarke of the Naval Research Laboratory in Washington DC; Craig Sarazin of the University of Virginia in Charlottesville, VA; Brian McNamara of the University of Waterloo in Waterloo, Canada; Edmund Douglass of Boston University and Michael McDonald of the University of Maryland, College Park, MD.

Fast Facts for Abell 2052:


Scale: Image is 9.3 arcmin across (about 1.27 million light years)
Category: Groups & Clusters of Galaxies
Coordinates: (J2000) RA 15h 16m 44.40s | Dec +07° 01' 20.00"
Constellation: Serpens
Observation Date: 11 pointings between Sept 2000 and June 2009
Observation Time: 183 hours 53 min (7 days 15 hours 53 min).
Obs. ID: 890, 5807, 10477-10480, 10879, 10914-10917
Color Code: X-ray (Blue); Optical (Orange)
Instrument: ACIS
References: Blanton, E. et al, 2011, ApJ 737:99
Distance Estimate: About 480 million light years (z=0.03549)

More about → Abell 2052: A Galaxy Cluster Gets Sloshed

Quadruply Lensed Dwarf Galaxy 12.8 Billion Light Years Away

Galaxy Cluster MACS J0329.6-0211 lenses several background galaxies including a distant dwarf galaxy. CREDIT: A. Zitrin, et al.

Gravitational lensing is a powerful tool for astronomers that allows them to explore distant galaxies in far more detail than would otherwise be allowed. Without this technique, galaxies at the edge of the visible universe are little more than tiny blobs of light, but when magnified dozens of times by foreground clusters, astronomers are able to explore the internal structural properties more directly.

Recently, astronomers at the University of Heidelberg discovered a gravitational lensed galaxy that ranked among the most distant ever seen. Although there’s a few that beat this one out in distance, this one is remarkable for being a rare quadruple lens.

The images for this remarkable discovery were taken using the Hubble Space Telescope in August and October of this year, using a total of 16 different colored filters as well as additional data from the Spitzer infrared telescope. The foreground cluster, MACS J0329.6-0211, is some 4.6 billion light years distant. In the above image, the background galaxy has been split into four images, labelled by the red ovals and marked as 1.1 – 1.4. They are enlarged in the upper right.

Assuming that the mass of the foreground cluster is concentrated around the galaxies that were visible, the team attempted to reverse the effects the cluster would have on the distant galaxy, which would reverse the distortions. The restored image, also corrected for redshift, is shown in the lower box in the upper right corner.

After correcting for these distortions, the team estimated that the total mass of the distant galaxy is only a few billion times the mass of the Sun. In comparison, the Large Magellanic Cloud, a dwarf satellite to our own galaxy, is roughly ten billion solar masses. The overall size of the galaxy was determined to be small as well. These conclusions fit well with expectations of galaxies in the early universe which predict that the large galaxies in today’s universe were built from the combination of many smaller galaxies like this one in the distant past.

The galaxy also conforms to expectations regarding the amount of heavy elements which is significantly lower than stars like the Sun. This lack of heavy elements means that there should be little in the way of dust grains. Such dust tends to be a strong block of shorter wavelengths of light such as ultraviolet and blue. Its absence helps give the galaxy its blue tint.

Star formation is also high in the galaxy. The rate at which they predict new stars are being born is somewhat higher than in other galaxies discovered around the same distance, but the presence of brighter clumps in the restored image suggest the galaxy may be undergoing some interactions, driving the formation of new stars.

Jon is a science educator currently living in Missouri. He is a high school teacher and does outreach with the St. Louis Astronomical society as well as presenting talks on science and related topics at regional conventions. He graduated from the University of Kansas with his BS in Astronomy in 2008 and has maintained the Angry Astronomer blog since 2006. For more of his work, you can find his website here.

Source: Universe Today

More about → Quadruply Lensed Dwarf Galaxy 12.8 Billion Light Years Away

Ambitious Hubble Survey Obtaining New Dark Matter Census

MACS J1206.2-0847
Credit: NASA, ESA, M. Postman (STScI), and the CLASH Team

This image of galaxy cluster MACS J1206.2-0847 (or MACS 1206 for short) is part of a broad survey with NASA's Hubble Space Telescope.

The distorted shapes in the cluster are distant galaxies from which the light is bent by the gravitational pull of an invisible material called dark matter within the cluster of galaxies. This cluster is an early target in a survey that will allow astronomers to construct the most detailed dark matter maps of more galaxy clusters than ever before.

These maps are being used to test previous, but surprising, results that suggest that dark matter is more densely packed inside clusters than some models predict. This might mean that galaxy cluster assembly began earlier than commonly thought.

The multiwavelength survey, called the Cluster Lensing And Supernova survey with Hubble (CLASH), probes, with unparalleled precision, the distribution of dark matter in 25 massive clusters of galaxies. So far, the CLASH team has completed observations of six of the 25 clusters.

Dark matter makes up the bulk of the universe's mass, yet it can only be detected by measuring how its gravity tugs on visible matter and warps space like a fun-house mirror so that the light from distant objects is distorted.

Galaxy clusters like MACS 1206 are perfect laboratories for studying dark matter's gravitational effects because they are the most massive structures in the universe. Because of their heft, the clusters act like giant cosmic lenses, magnifying, distorting and bending any light that passes through them — an effect known as gravitational lensing.

Lensing effects can also produce multiple images of the same distant object, as evident in this Hubble picture. In particular, the apparent numbers and shapes of distant galaxies far beyond a galaxy cluster become distorted as the light passes through, yielding a visible measurement of how much mass is in the intervening cluster and how it is distributed. The substantial lensing distortions seen are proof that the dominant component of clusters is dark matter. The distortions would be far weaker if the clusters' gravity came only from the visible galaxies in the clusters.

MACS 1206 lies 4.5 billion light-years from Earth. Hubble's keen vision helped CLASH astronomers uncover 47 multiple images of 12 newly identified faraway galaxies. Finding so many multiple images in a cluster is a unique capability of Hubble, and the CLASH survey is optimized to find them. The new observations build on earlier work by Hubble and ground-based telescopes.

Taking advantage of two of Hubble's powerful cameras, the Advanced Camera for Surveys and the Wide Field Camera 3, the CLASH survey covers a broad wavelength range, from ultraviolet to near infrared. Astronomers need the diverse colors to estimate the distances to lensed galaxies and study them in more detail. Hubble's unique capabilities allow astronomers to estimate distances to galaxies that are four times fainter than ground-based telescopes can see.

The era when the first clusters formed is not precisely known, but is estimated to be at least 9 billion years ago and possibly as far back as 12 billion years ago. If most of the clusters in the CLASH survey are found to have excessively high accumulations of dark matter in their central cores, then it may yield new clues to the early stages in the origin of structure in the universe.

Future telescopes like NASA's James Webb Space Telescope, a space-based infrared observatory now being built, will be able to study the fainter lensed galaxies in clusters like MACS 1206 in greater detail. Webb will be powerful enough to collect the spectra of some of the magnified galaxies to study their early chemical composition.

For additional information, contact:

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Marc Postman
Space Telescope Science Institute, Baltimore, Md.
410-338-4340
postman@stsci.edu

More about → Ambitious Hubble Survey Obtaining New Dark Matter Census