Posted on by Tammy Plotner

Subaru Telescope Reveals Orderly Massive Galaxy Evolution

FMOS spectra in the J-band (left panel) and H-band (right panel), each of which filters light so that only specific wavelengths can pass through. The horizontal axis refers to the wavelength direction while the vertical axis indicates individual spectra observed through each fiber. Small blue circles indicate the detection of emission lines (left: H? and [OIII]; right: H?, [NII]). The inset box shows the intensity of the emission lines for one galaxy. The vertical bands indicate the masked regions where bright sky (OH) emissions are prevented from entering science fibers placed on high-redshift galaxies. (Credit: FMOS-COSMOS)

Nobody likes a sloppy COSMOS (Cosmological Evolution Survey) and astronomers utilizing the Fiber-Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope have put order into chaos through their studies. The survey has found that some nine billion years ago galaxies were capable of producing new stars in a fashion as orderly as game of checkers. Despite their young cosmological age, the galaxies show signs containing high amounts of dust enriched by heavier elements – a mature state.

“These findings center on a major question: What was the universe like when it was maximally forming its stars?” says John Silverman, the principal investigator of the FMOS-COSMOS project at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU).

These “universal” questions are just what the COSMOS team seeks to answer. Their research goals are to enlighten the scales of cosmic time in relationship with the environment, formation and evolution of massive galactic structures. When studying individual galaxies, they may be able to tell if their rate of growth can be attributed to large-scale environments. Information of this type can clarify what factors the early Universe structure may have contributed to the current form of local galaxies. One of the data sets the team is focusing on is using the FMOS on the Subaru Telescope to chart out the distribution of more than a thousand galaxies which formed over nine billion years ago – a time when the Universe was hitting its star-formation peak.

“One key to generating fruitful results is collaboration between COSMOS researchers to maximize optimal use of FMOS.” Silverman continues, “In this project, researchers from Kavli IPMU in Japan and the Institute for Astronomy at the University of Hawaii (principal investigator: David Sanders) formed an effective collaboration to implement their goal.” The observations spanned 10 clear nights starting in March 2012.

Why choose spectroscopy? This advanced fiber optics technology speaks for itself, collecting light over an area of sky equal in size to that of the Moon. The FMOS focuses on the near-infrared, filtering out unwanted emissions caused by warm temperatures and can acquire spectra from 400 galaxies simultaneously with a wide field of coverage of 30 arc minutes at prime-focus. By employing such a wide field of view, astronomers can squeeze in a wide range of objects in their local environments. This enables researchers to maximize information on star-forming regions, cluster formation, and cosmology.

As David Sanders, the principal investigator of the FMOS-COSMOS project at IfA, puts it, “FMOS has clearly revolutionized our ability to study how galaxies form and evolve across cosmic time. It is currently the most powerful instrument we have to study the large numbers of objects needed to understand galaxies of all sizes, shapes and masses — from the largest ellipticals to the smallest dwarfs. We are extremely fortunate that the Kavli IPMU-IfA collaboration is giving us this unique opportunity to study the distant universe in such exquisite detail.”

FMOS will soon be famous by revealing its true potential. It has been collecting copious amounts of data in a high spectral resolution mode and at a very successful rate. So far it has accomplished nearly half of its goal – to examine over a thousand galaxies with redshifts to map the large-scale structure. The current survey consists of mapping an area of sky which spans a square degree in high-resolution mode and future plans for FMOS will involve enlarging the area. This expanded coverage will complement other instruments on alternative telescopes which have a wider spectral imaging system or a higher resolution which is limited to a smaller area. These combined findings may one day result in showing us some of the very first structures that eventually evolved into the massive galaxy clusters we see today!

Original Story Source: Kavli Institute for the Physics and Mathematics of the Universe News Release.

Posted on by John Williams

Surprise! Galaxies Still Evolving in Present Universe

A giant spiral of gas dust and stars, Messier 101 spans 170,000 light-years and contains more than a trillion stars. Astronomers have uncovered a surprising trend in galaxy evolution where galaxies like M101 and the Milky Way Galaxy continued to develop into settled disk galaxies long after previously thought. Credit: NASA/ESA Hubble

Graceful in their turnings, spiral galaxies were thought to have reached their current state billions of years ago. A study of hundreds of galaxies, however, upsets that notion revealing that spiral galaxies, like the Andromeda Galaxy and our own Milky Way, have continued to change.

“Astronomers thought disk galaxies in the nearby universe had settled into their present form by about 8 billion years ago, with little additional development since,” said Susan Kassin, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Md., and the study’s lead researcher in a press release. “The trend we’ve observed instead shows the opposite, that galaxies were steadily changing over this time period.”

A study of 544 star-forming galaxies observed by the Earth-based Keck and Hubble Space Telescope shows that disk galaxies like our Milky Way Galaxy unexpectedly reached their current state long after much of the universe’s star formation had ceased. Credit: NASA’s Goddard Space Flight Center

Astronomers used the twin 10-meter earth-bound W.M. Keck Observatory atop Hawaii’s Mauna Kea volcano and NASA’s Hubble Space Telescope to study 544 star-forming galaxies. Farther back in time, galaxies tend to be very different, say astronomers, with random and disorganized motions. Nearer to the present, star-forming galaxies look like well-ordered disk-shaped systems. Rotation in these galaxies trumps other internal, random motions. These galaxies are gradually settling into well-behaved disks with the most massive galaxies always showing higher organization.

This plot shows the fractions of settled disk galaxies in four time spans, each about 3 billion years long. There is a steady shift toward higher percentages of settled galaxies closer to the present time. At any given time, the most massive galaxies are the most settled. More distant and less massive galaxies on average exhibit more disorganized internal motions, with gas moving in multiple directions, and slower rotation speeds. Credit: NASA’s Goddard Space Flight Center

The sampling of galaxies studied, from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey, ranged between 2 billion and 8 billion light-years from Earth with masses between 0.3 percent to 100 percent that of our own Milky Way Galaxy. Researchers looked at all galaxies in this time range with emission lines bright enough to determine internal motions. Researchers focused on emission lines characteristically emitted by gas within the galaxy. The emission lines not only tell scientists about the elements that make up the galaxies but also red shifting of emission lines contains information on the internal motions and distance.

“Previous studies removed galaxies that did not look like the well-ordered rotating disks now common in the universe today,” said co-author Benjamin Weiner, an astronomer at the University of Arizona in Tucson. “By neglecting them, these studies examined only those rare galaxies in the distant universe that are well-behaved and concluded that galaxies didn’t change.”

In the past 8 billion years, mergers between galaxies, both large and small, has decreased. So has the overall rate of star formation and associated disruptions due to supernovae explosions. Both factors may play a role in the newly found trend, say scientists.

The Milky Way Galaxy may have gone through the same chaotic growing and changing as the galaxies in the DEEP2 sample before settling into its present state at just about the same time the Sun and Earth were forming, say team scientists. By observing the pattern, astronomers can now adjust computer simulations of galaxy evolution until they replicate the observations. Then the hunt will be on to determine the physical processes responsible for the trend.

This cosmological simulation follows the development of a single disk galaxy throughout the life of the Universe; about 13.5 billion years. Red colors show old stars, young stars show as white and bright blue while the distribution of gas shows as a pale blue. The computer-generated view spans about 300,000 light-years. The simulation, running on the Pleiades supercomputer at NASA’s Ames Research Center in Moffett Field, California, took about 1 million CPU hours to complete. Credit: F. Governato and T. Quinn (Univ. of Washington), A. Brooks (Univ. of Wisconsin, Madison), and J. Wadsley (McMaster Univ.).

A paper detailing the findings will be published in the October 20, 2012 The Astrophysical Journal.

Source: NASA

Posted on by Nancy Atkinson

Bright Stars Don’t Like to Be Alone

Caption: New research using data from European Southern Observatory telescopes, including the Very Large Telescope, has revealed that the hottest and brightest stars, known as O stars, are often found in close pairs. Credit: ESA, NASA, H. Sana (Amsterdam University), and S.E. de Mink (STScI)

Like humans, stars seem to prefer the company of companions. A new study using the Very Large Telescope reveals that most very bright, high-mass O-type stars do not live alone. Surprisingly, almost three-quarters of these stars have a close companion star, far more than previously thought. But sometimes – also like humans – the relationship between companion stars can turn a little ugly, with one star becoming dominant and even disruptive by stealing matter from the other, or doing a hostile takeover.


An international team of astronomers have found that some stars will virtually suck the life out of another, and about one-third of the time, a pair of stars will ultimately merge to form a single star.

The stars included in this study are some of the biggest, brightest stars which have very high temperatures. They live fast and die young, and in their lives play a key role in the evolution of galaxies. by, which drive the evolution of galaxies. They are also linked to extreme phenomena such as gamma-ray bursts.

“These stars are absolute behemoths,” said Hugues Sana, from the University of Amsterdam, The Netherlands, lead author of the study. “They have 15 or more times the mass of our Sun and can be up to a million times brighter. These stars are so hot that they shine with a brilliant blue-white light and have surface temperatures over 54,000 degrees Fahrenheit (30,000 degrees C).”

The astronomers studied a sample of 71 O-type single stars and stars in pairs (binaries) in six nearby young star clusters in the Milky Way.
By analyzing the light coming from these targets in greater detail than before, the team discovered that 75 percent of all O-type stars exist inside binary systems, a higher proportion than previously thought, and the first precise determination of this number. More importantly, though, they found that the proportion of these pairs that are close enough to interact (through stellar mergers or transfer of mass by so-called vampire stars) is far higher than anyone had thought, which has profound implications for our understanding of galaxy evolution.

O-type stars make up just a fraction of a percent of the stars in the universe, but the violent phenomena associated with them mean they have a disproportionate effect on their surroundings. The winds and shocks coming from these stars can both trigger and stop star formation, their radiation powers the glow of bright nebulae, their supernovae enrich galaxies with the heavy elements crucial for life, and they are associated with gamma-ray bursts, which are among the most energetic phenomena in the universe. O-type stars are therefore implicated in many of the mechanisms that drive the evolution of galaxies.

“The life of a star is greatly affected if it exists alongside another star,” said Selma de Mink of the Space Telescope Science Institute, in Baltimore, Md., a co-author of the study. “If two stars orbit very close to each other they may eventually merge. But even if they don’t, one star will often pull matter off the surface of its neighbor.”

Mergers between stars, which the team estimates will be the ultimate fate of around 20 to 30 percent of O-type stars, are violent events. But even the comparatively gentle scenario of vampire stars, which accounts for a further 40 to 50 percent of cases, has profound effects on how these stars evolve.

Until now, astronomers mostly considered that closely orbiting massive binary stars were the exception, something that was only needed to explain exotic phenomena such as X-ray binaries, double pulsars, and black hole binaries. The new study shows that to properly interpret the universe, this simplification cannot be made: these heavyweight double stars are not just common, their lives are fundamentally different from those of single stars.

Loading player…

For instance, in the case of vampire stars — where the smaller, lower-mass star is rejuvenated as it sucks the fresh hydrogen from its companion — its mass will increase substantially and it will outlive its companion, surviving much longer than a single star of the same mass. The victim star, meanwhile, is stripped of its envelope before it has a chance to become a luminous red supergiant. Instead, its hot, blue core is exposed. As a result, the stellar population of a distant galaxy may appear to be much younger than it really is: both the rejuvenated vampire stars, and the diminished victim stars become hotter, and bluer in color, mimicking the appearance of younger stars. Knowing the true proportion of interacting high-mass binary stars is therefore crucial to correctly characterize these faraway galaxies.

“The only information astronomers have on distant galaxies is from the light that reaches our telescopes. Without making assumptions about what is responsible for this light we cannot draw conclusions about the galaxy, such as how massive or how young it is. This study shows that the frequent assumption that most stars are single can lead to the wrong conclusions,” said Sana.

Understanding how big these effects are, and how much this new perspective will change our view of galactic evolution, will need further work. Modeling binary stars is complicated, so it will take time before all these considerations are included in models of galaxy formation.

The paper was published in the July 27 issue of the journal Science.

Paper by: Sana, de Mink, et al. (PDF document)

Sources: ESO, HubbleSite

Posted on by Tammy Plotner

The Care And Feeding Of Teenage Galaxies… And By The Way, They Need Gas

Images of the six galaxies with detected inflows taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Most of these galaxies have a disk-like, spiral structure, similar to that of the Milky Way. Star formation activity occurring in small knots is evident in several of the galaxies' spiral arms. Because the spirals appear tilted in the images, Rubin et al. concluded that we are viewing them from the side, rather than face-on. This orientation meshes well with a scenario of 'galactic recycling' in which gas is blown out of a galaxy perpendicular to its disk, and then falls back in at different locations along the edge of the disk. Credit: K. Rubin, MPIA

[/caption]

Got a teenager? Then you know the story. Go to look for your favorite bag of chips and they’re gone. You eat one portion of meat and they need three. If you like those cookies, then you better have a darn good place to stash them. And, while you’re at it, their car needs gas. Apparently there’s a reason for the word “universal”, because teenage galaxies aren’t much different. Thanks to some new studies done by ESO’s Very Large Telescope, astronomers have been able to take a much closer look at adolescent galaxies and their “feeding habits” during their evolution. Some 3 to 5 billion years after the Big Bang they were happiest when just provided with gas, but later on they developed a voracious appetite… for smaller galaxies!

Scientists have long been aware that early galaxy structures were much smaller than the grand spirals and hefty ellipticals which fill the present Universe. However, figuring out exactly how galaxies put on weight – and where the bulk supply comes from – has remained an enigma. Now an international group of astronomers have taken on more than a hundred hours of observations taken with the VLT to help determine how gas-rich galaxies developed.

“Two different ways of growing galaxies are competing: violent merging events when larger galaxies eat smaller ones, or a smoother and continuous flow of gas onto galaxies.” explains team leader, Thierry Contini (IRAP, Toulouse, France). “Both can lead to lots of new stars being created.”

The undertaking is is MASSIV – the Mass Assembly Survey with the VIsible imaging Multi-Object Spectrograph, a powerful camera and spectrograph on the VLT. It’s incredible equipment used to measure distance and properties of the surveyed galaxies Not only did the survey observe in the near infrared, but also employed a integral field spectrograph and adaptive optics to refine the images. This enables astronomers to map inner galaxy movements and content, as well as leaving room for some very surprising results.

“For me, the biggest surprise was the discovery of many galaxies with no rotation of their gas. Such galaxies are not observed in the nearby Universe. None of the current theories predict these objects,” says Benoît Epinat, another member of the team.

“We also didn’t expect that so many of the young galaxies in the survey would have heavier elements concentrated in their outer parts — this is the exact opposite of what we see in galaxies today,” adds Thierry Contini.

These results point towards a major change during the galactic “teenage years”. At some time during the young Universe state, smooth gas flow was a considerable building block – but mergers would later play a more important role.

“To understand how galaxies grew and evolved we need to look at them in the greatest possible detail. The SINFONI instrument on ESO’s VLT is one of the most powerful tools in the world to dissect young and distant galaxies. It plays the same role that a microscope does for a biologist,” adds Thierry Contini.

The team plans on continuing to study these galaxies with future instruments on the VLT as well as using ALMA to study the cold gas in these galaxies. However, their work with gas isn’t the only “station” on the block. In a separate study led by Kate Rubin (Max Planck Institute for Astronomy), the Keck I telescope on Mauna Kea, Hawaii, has been used to examine gas associated with a hundred galaxies at distances between 5 and 8 billion light-years – the older teens. They have found initial evidence of gas flowing back into distant galaxies that are actively forming new stars.

Images of the six galaxies with detected inflows taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Most of these galaxies have a disk-like, spiral structure, similar to that of the Milky Way. Star formation activity occurring in small knots is evident in several of the galaxies' spiral arms. Because the spirals appear tilted in the images, Rubin et al. concluded that we are viewing them from the side, rather than face-on. This orientation meshes well with a scenario of 'galactic recycling' in which gas is blown out of a galaxy perpendicular to its disk, and then falls back in at different locations along the edge of the disk. Credit: K. Rubin, MPIA

Apparently, like a teenager with the munchies, matter finds its way into those galactic tummies. One feeding theory is an inflow from huge low-density gas reservoirs filling the intergalactic voids… another is huge cosmic matter cycle. While there is very little evidence to support either hypothesis, gases have been observed to flow away from some galaxies and may be moshed around by several different sources – such as supernovae events or peer pressure from gigantic stars.

“As this gas drifts away, it is pulled back by the galaxy’s gravity, and could re-enter the same galaxy in time scales of one to several billion years. This process might solve the mystery: the gas we find inside galaxies may only be about half of the raw material that ends up as fuel for star formation.” says Dr. Rubin. “Large amounts of gas are caught in transit, but will re-enter the galaxy in due time. Add up the galaxy’s gas and the gas currently undergoing cosmic recycling, and there is a sufficient amount of raw matter to account for the observed rates of star formation.”

It might very well be a case of cosmic recycling… but I’d feel safer hiding my cookies.

Original Story Sources: ESO News Release and MPIA Science News Release. For Further Reading: Research Paper 1, Research Paper 2, Research Paper 3 and Research Paper 4.

Posted on by Tammy Plotner

FourStar Service: Red Galaxy Cluster Hides In Plain Sight

An infared image of the cluster. Three narrow slices of the infrared spectrum are represented in this color composite. The colors have been balanced to accentuate the red galaxies at a distance of 10.5 billion light years. Credit: FourStar Galaxy Evolution Survey ("Z-FOURGE")

[/caption]

Located some 10.5 billion light years away in the general direction of the constellation of Leo, the most distant cluster of red galaxies so far discovered has been hiding in plain sight… until now. Thanks to the advanced observing techniques of FourStar, a new and powerful near-infrared camera on the 6.5m Magellan Baade Telescope, we’re now able to peer beyond faint and into the realm of the faintest. It’s 30 galaxies packed like sardines in a tin and their formation is the earliest known “galaxy city” in the Universe!

“These are the first steps of accurately measuring the rate at which these large urban cities formed in a dark-matter-dominated universe,” says Texas A&M astronomer, Dr. Casey Papovich. “The rate at which they come together tests our understanding of how structures in the universe formed. The broader the timeline, the better our chances of being accurate. Instrumentation is key, and as it evolves, we’ll keep pushing the boundaries.”

Up until now, this galaxy conglomeration had remained undisclosed – despite thousand upon thousands of hours of survey images taken in their area. It is truly amazing that they were overlooked by the huge ground-based telescopes and space-based research instruments, including the Hubble Space Telescope. There was just no accurate distance estimations until the FourStar project came along. Headed by Eric Persson of the Carnegie Observatories, the stellar team includes Carnegie’s David Murphy, Andy Monson, Dan Kelson, Pat McCarthy, and Ryan Quadri – a group whose findings will be published in the Astrophysical Journal Letters.

Just what is FourStar? It’s a specialized camera set with a group of five very specific filters which are sensitively tuned to a very narrow portion of the near-infrared spectrum. “These new filters are a novel approach; it’s a bit like being able to do a CAT scan of the sky to rapidly make a 3-D picture of the early universe,” says Swinburne’s Karl Glazebrook, who is leading the Australian component of the international collaboration formed in 2009.What sets it apart is its ability to accurately measure distances between Earth and target galaxies one at a time. This allows the program to build an incredible three-dimensional look at the source point.

“Most other surveys were just looking at the tip of the iceberg,” Dr. Kim-Vy Tran explains. “The modern technology contained in this camera enabled us to detect the faintest light possible, allowing us to see much more of the iceberg than previously revealed. It’s like we’re using a comb to sift through the very distant universe. The combination of filters and depth provided by this camera give us the equivalent of more teeth, resulting in better measurements and more accurate results.”

The survey was built one deep over an 11×11 arcminute field each in COSMOS, CDFS and UDS. When it comes to galaxy properties, they are looking at 1-2% accurate redshifts and the current 3-D map is looking back to when the Universe was only 3 billion years old.

“This means the galaxy cluster is still young and should continue to grow into an extremely dense structure possibly containing thousands of galaxies,” explained lead author Lee Spitler of Australia’s Swinburne University of Technology.

The FourStar Galaxy Evolution Survey (“Z-FOURGE”) is just the beginning. Through studies of clusters like this one, astronomers can and will get a better understanding of how galaxy clusters evolve in relationship to their environments and – possibly – how they assemble into larger structures. The survey, led by Dr. Ivo Labbé, a former Carnegie postdoctoral fellow, now at Leiden Observatory in the Netherlands, will also strengthen our abilities to determine distances. In just a half a year, the team “has obtained accurate distances for faint galaxies over a region roughly one-fifth the apparent size of the Moon” locating about another thousand galaxies at even further extents.

“The excellent image quality and sensitivity of Magellan and FourStar really make the difference,” Labbé said. “We look forward to many more exciting and unexpected discoveries!”

Original Story Source: Carnegie Science News Release.

Posted on by Tammy Plotner

Galactic Archaeology: NGC 5907 – The Dragon Clash

NGC 5907 - Credit: R. Jay Gabany

[/caption]

The sprawling northern constellation of Draco is home to a monumental galactic merger which left a singular spectacle – NGC 5907. Surrounded by an ethereal garment of wispy star trails and currents of stellar material, this spiral galaxy is the survivor of a “clash of the dragons” which may have occurred some 8 to 9 billion years ago. Recent theory suggests galaxies of this type may be the product of a larger galaxy encountering a smaller satellite – but this might not be the case. Not only is NGC 5907 a bit different in some respects, it’s a lot different in others… and peculiar motion is just the beginning.

“If the disc of many spirals is indeed rebuilt after a major merger, it is expected that tidal tails can be a fossil record and that there should be many loops and streams in their halos. Recently Martínez-Delgado et al. (2010) have conducted a pilot survey of isolated spiral galaxies in the Local Volume up to a low surface brightness sensitivity of ~28.5 mag/arcsec2 in V band. They find that many of these galaxies have loops or streams of various shapes and interpret these structures as evidence of minor merger or satellite infall.” says J. Wang of the Chinese Academy of Sciences. “However, if these loops are caused by minor mergers, the residual of the satellite core should be detected according to numerical simulations. Why is it hardly ever detected?”

The “why” is indeed the reason NGC 5907 is being intensively studied by a team of six scientists of the Observatoire de Paris, CNRS, Chinese Academy of Sciences, National Astronomical Observatories of China NAOC and Marseille Observatory. Even though NGC 5907 is a member of a galactic group, there are no galaxies near enough to it to be causing an interaction which could account for its streamers of stars. It is truly a warped galaxy with gaseous and stellar disks which extend beyond the nominal cut-off radius. But that’s not all… It also has a peculiar halo which includes a significant fraction of metal enriched stars. NGC 5907 just doesn’t fit the patterns.

“For some of our models, we assume a star formation history with a varying global efficiency in transforming gas to stars, in order to preserve enough gas from being consumed before fusion.” explains the research team. “Although this fine-tuned star formation history may have some physical motivations, its main role is also to ensure the formation of stars after the emergence of the gaseous disc just after fusion.”

On left, the NGC 5907 galaxy. It is compared to the simulations, on right. Both cases show an edge-on galactic disk surrounded by giant loops of old stars, which are witnessing of a former, gigantic collision. (Jay Gabany, cosmotography.com / Observatoire de Paris / CNRS / Pythéas / NAOC)

Now enter the 32- and 196-core computers at the Paris Observatory center and the 680-core Graphic Processor Unit supercomputer of Beijing NAOC with the capability to run 50000 billion operations per second. By employing several state of the art, hydrodynamical, and numerical simulations with particle numbers ranging from 200 000 to 6 millions, the team’s goal was to show the structure of NGC 5907 may have been the result of the clash of two dragon-sized galaxies… or was it?

“The exceptional features of NGC 5907 can be reproduced, together with the central galaxy properties, especially if we compare the observed loops to the high-order loops expected in a major merger model.” says Wang. “Given the extremely large number of parameters, as well as the very numerous constraints provided by the observations, we cannot claim that we have already identified the exact and unique model of NGC 5907 and its halo properties. We nevertheless succeeded in reproducing the loop geometry, and a disc-dominated, almost bulge-less galaxy.”

In the meantime, major galaxy merger events will continue to be a top priority in formation research. “Future work will include modelling other nearby spiral galaxies with large and faint, extended features in their halos.” concludes the team. “These distant galaxies are likely similar to the progenitors, six billion years ago, of present-day spirals, and linking them together could provide another crucial test for the spiral rebuilding disc scenario.”

And sleeping dragons may one day arise…

Original Story Source: Paris Observatory News. For Further Reading: Loops formed by tidal tails as fossil records of a major merger and Fossils of the Hierarchical Formation of the Nearby Spiral Galaxy NGC 5907.

Posted on by Tammy Plotner

Young Star Cluster In Disintegrated Galaxy Reveals First-Ever Intermediate Mass Black Hole

This spectacular edge-on galaxy, called ESO 243-49, is home to an intermediate-mass black hole that may have been stripped off of a cannibalized dwarf galaxy. Credit: NASA, ESA, and S. Farrell (Sydney Institute for Astronomy, University of Sydney)

[/caption]

Score another first for NASA’s Hubble Space Telescope! Along with observations taken with the Swift X-ray telescope, a team of astronomers have identified a young stellar cluster of stars pointing the way towards the first verified intermediate mass black hole. This grouping of stars provides significant indication that black holes of this type may have been at the center of a now shredded dwarf galaxy – a finding which increases our knowledge of galaxy evolution.

“For the first time, we have evidence on the environment, and thus the origin, of this middle-weight black hole,” said Mathieu Servillat, a member of the Harvard-Smithsonian Center for Astrophysics research team.

Designated as ESO 243-49 HLX-1, this incredible intermediate mass black hole was discovered in 2009 by Sean Farrell, of the Sydney Institute for Astronomy in Australia, using the European Space Agency’s XMM-Newton X-ray space telescope. Hyper-Luminous X-ray Source 1 is a 20,000 solar mass beauty which resides at the edge of galaxy ESO 243-49 some 290 million light years away. However, the Newton’s findings weren’t the only contribution – HLX-1 was also verified with NASA’s Swift observatory in X-ray and Hubble in near-infrared, optical, and ultraviolet wavelengths. What stands out is the presence of a cluster of young stars encircling the black hole and stretching out across about 250 light years of space. While the stars themselves are too far away to be resolved, their magnitude and spectra match with other young clusters seen in similar galaxies.

Just what clued the team to the presence of a star cluster? In this case their instruments revealed the blue spectrum of hot gases being emitted from the accretion disk located at the periphery of the black hole… and there was more. They also noted the presence of red light spawned by cooler gases which may indicate the presences of stars. Time to match up the findings against computer modeling.

“What we can definitely say with our Hubble data is that we require both emission from an accretion disk and emission from a stellar population to explain the colors we see.” said Farrell.

Why is the presence of a young star cluster unusual? According to what we know so far, they just don’t occur outside a flattened disk such as HLX-1. This finding may indicate the intermediate mass black hole may have once been at the heart of a dwarf galaxy engaged in a merger event. The dwarf galaxy’s stars were stripped away, but not its capabilities to form new. During the interaction, the gas around the black hole was compressed and star formation began again… but how long ago?

“The age of the population cannot be uniquely constrained, with both very young and very old stellar populations allowed. However, the very old solution requires excessively high levels of disc reprocessing and an extremely small disc, leading us to favour the young solution with an age of ~13 Myr.” says the team. “In addition, the presence of dust lanes and the lack of any nuclear activity from X-ray observations of the host galaxy lead us to propose that a gas-rich minor merger may have taken place less than ~200 Myr ago. Such a merger event would explain the presence of the intermediate mass black hole and support a young stellar population.”

Discoveries such as HLX-1 will help astronomers further understand how supermassive black holes are formed. Current conjecture is that intermediate mass black holes may migrate together to form their larger counterparts. Studying the trajectory of this new find may provide valuable information… even if it is unknown at this point. HLX-1 may be drawn into a merger event and it may just end up orbiting ESO 243-49. Regardless of what happens, chances are it will fade away in X-ray as it exhausts its gas supply.

“This black hole is unique in that it’s the only intermediate-mass black hole we’ve found so far. Its rarity suggests that these black holes are only visible for a short time,” said Servillat.

Original Story Source: Harvard Center for Astrophysics News Release. For Further Reading: A Young Massive Stellar Population Around the Intermediate Mass Black Hole ESO 243-49 HLX-1.

Posted on by Tammy Plotner

Deep Blue Astrophotography – Imaging Galactic Shells

NGC7600 is an elliptical galaxy and is around 50 Mpc in distance. This image shows an interleaved system of shells that are described in this Astronomical Journal Letters here. These types of structures around elliptical galaxies were first revealed by Malin & Carter in 1980. This deep image of NGC7600 shows faint features not previously seen. Credit: Ken Crawford

[/caption]

As a professional astronomy journalist, I read a lot of science papers. It hasn’t been all that long ago that I remember studying about galaxy groups – with the topic of dark matter and dwarf galaxies in particular. Imagine my surprise when I learn that two of my friends, who are highly noted astrophotographers, have been hard at work doing some deep blue science. If you aren’t familiar with the achievements of Ken Crawford and R. Jay Gabany, you soon will be. Step inside here and let us tell you why “it matters”…

According to Ken’s reports, Cold Dark Matter (or CDM) is a theory that most of the material in the Universe cannot be seen (dark) and that it moves very slowly (cold). It is the leading theory that helps explain the formation of galaxies, galaxy groups and even the current known structure of the universe. One of the problems with the theory is that it predicts large amounts of small satellite galaxies called dwarf galaxies. These small galaxies are about 1000th the mass of our Milky Way but the problem is, these are not observed. If this theory is correct, then where are all of the huge amounts of dwarf galaxies that should be there?

Enter professional star stream hunter, Dr. David Martinez-Delgado. David is the principal investigator of the Stellar Tidal Stream Survey at the Max-Planck Institute in Heidelberg, Germany. He believes the reason we do not see large amounts of dwarf galaxies is because they are absorbed (eaten) by larger galaxies as part of the galaxy formation. If this is correct, then we should find remnants of these mergers in observations. These remnants would show up as trails of dwarf galaxy debris made up mostly of stars. These debris trails are called star streams.

“The main aim of our project is to check if the frequency of streams around Milky Way-like galaxies in the local universe is consistent with CDM models similar to that of the movie.” clarifies Dr. Martinez-Delgado. “However, the tidal destruction of galaxies is not enough to solve the missing satellite problem of the CDM cosmology. So far, the best given explanation is that some dark matter halos are not able to form stars inside, that is, our Galaxy would surround by a few hundreds of pure dark matter satellites.”

Enter the star stream hunters professional team. The international team of professional astronomers led by Dr. David Martinez-Delgado has identified enormous star streams on the periphery of nearby spiral galaxies. With deep images he showed the process of galactic cannibalism believed to be occurring between the Milky Way and the Sagittarius dwarf galaxy. This is in our own back yard! Part of the work is using computer modeling to show how larger galaxies merge and absorb the smaller ones.

This image has been inverted and contrast enhanced to help display the faint shell features and debris fragments. The farthest fragment is 140 kpc in projection from the center of the galaxy. Credit: Ken Crawford
“Our observational approach is based on deep color-magnitude diagrams that provide accurate distances, surface brightness, and the properties of stellar population of the studied region of this tidal stream.” says Dr. Martinez-Delgado (et al). “These detections are also strong observational evidence that the tidal stream discovered by the Sloan Digitized Sky Survey is tidally stripped material from the Sagittarius dwarf and support the idea that the tidal stream completely enwraps the Milky Way in an almost polar orbit. We also confirm these detections by running numerical simulations of the Sagittarius dwarf plus the Milky Way. This model reproduces the present position and velocity of the Sagittarius main body and presents a long tidal stream formed by tidal interaction with the Milky Way potential.”

Enter the team of amateurs led by R. Jay Gabany. David recruited a small group of amateur astrophotographers to help search for and detect these stellar fossils and their cosmic dance around nearby galaxies, thus showing why there are so few dwarf galaxies to be found.

“Our observations have led to the discovery of six previously undetected, gigantic, stellar structures in the halos of several galaxies that are likely associated with debris from satellites that were tidally disrupted far in the distant past. In addition, we also confirmed several enormous stellar structures previously reported in the literature, but never before interpreted as being tidal streams.” says the team. “Our collection of galaxies presents an assortment of tidal phenomena exhibiting strikingly diverse morphological characteristics. In addition to identifying great circular features that resemble the Sagittarius stream surrounding the Milky Way, our observations have uncovered enormous structures that extend tens of kiloparsecs into the halos of their host’s central spiral. We have also found remote shells, giant clouds of debris within galactic halos, jet-like features emerging from galactic disks and large-scale, diffuse structures that are almost certainly related to the remnants of ancient, already thoroughly disrupted satellites. Together with these remains of possibly long defunct companions, our survey also captured surviving satellites caught in the act of tidal disruption. Some of these display long tails extending away from the progenitor satellite very similar to the predictions forecasted by cosmological simulations.”

The .5 meter Ritchey-Chretien Telescope of the Blackbird Observatory is situated at 7300 ft.(2225 meters) elevation under spectacularly clear and dark skies in the south central Sacramento Mountains of New Mexico, near Mayhill. Photo credit: R. Wodaski

Can you imagine how exciting it is to be part of deep blue science? It is one thing to be a good astrophotographer – even to be an exceptional astrophotographer – but to have your images and processing to be of such high quality as to be contributory to true astronomical research would be an incredible honor. Just ask Ken Crawford…

“Several years ago I was asked to become part of this team and have made several contributions to the survey. I am excited to announce that my latest contribution has resulted in a professional letter that has been recently accepted by the Astronomical Journal.” comments Ken. “There are a few things that make this very special. One, is that Carlos Frenk the director of the Institute for Computational Cosmology at Durham University (UK) and his team found that my image of galaxy NGC7600 was similar enough to help validate their computer model (simulation) of how larger galaxies form by absorbing satellite dwarf galaxies and why we do not see large number of dwarf galaxies today.”

Dr. Carlos Frenk has been featured on several television shows on the Science and Discovery channels, to name a few, to explain and show some of these amazing simulations. He is the director of the Institute for Computational Cosmology at Durham University (UK), was one of the winners of the 2011 Cosmology Prize of The Peter and Patricia Gruber Foundation.

“The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability.” says Frenk (et al). “Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations.”

The Rancho Del Sol Observatory is located in the foothills of the northern California's Sierra Mountains approximately one hour north of Sacramento. It houses a .5 meter Ritchey-Chretien Telescope. Credit: Ken Crawford
And it requires very accurate depictions of studies. According to the team, this pilot survey was conducted with three privately owned observatories equipped with modest sized telescopes located in the USA and Australia. Each observing site features very dark, clear skies with seeing that is routinely at and often below 1.5 arcseconds. These telescopes are manufactured by RC Optical Systems and follow a classic Ritchey-Chretien design. The observatories are commanded with on-site computers that allow remote operation and control from any global location with highband web accesses. Each observatory uses proven, widely available remote desktop control software. Robotic orchestration of all observatory and instrument functions, including multiple target acquisition and data runs, is performed using available scripting software. Additional use of a wide field instrument was employed for those galaxies with an extended angular size. For this purpose, they selected the Astro Physics Starfire 160EDF6, a short focal length (f/7) 16 cm aperture refractor that provides a FOV of 73.7 × 110.6 arcmin. But, it’s more than just taking a photograph. The astrophotographer needs to completely understand what needs to be drawn out of the exposure. It’s more than just taking a “pretty picture”… it’s what matters.

The formation of shell galaxies in the cold dark matter universe from Kenneth Crawford on Vimeo.

“The galaxy I want to show you has some special features called ‘shells’. I had to image very deep to detect these structures and carefully process them so you can see the delicate structures within.” explains Crawford. “The galaxy name is NGC7600 and these shell structures have not been captured as well in this galaxy before. The movie above shows my image of NGC7600 blending into the simulation at about the point when the shells start to form. The movie below shows the complete simulation.”

“What is ground breaking is that the simulation uses the cold dark matter theory modeling the dark matter halos of the galaxies and as you can see, it is pretty convincing.” concludes Crawford. “So now you all know why we do not observe lots of dwarf galaxies in the Universe.”

But, we can observe some very incredible science done by some very incredible friends. It’s what matters…

For Further Reading: Tracing Out the Northern Tidal Stream of the Sagittarius Dwarf Spheroidal Galaxy, Stellar Tidal Streams in Spiral Galaxies of the Local Volume, Carlos Frenk, Simulations of the formation, evolution and clustering of galaxies and quasars, The formation of shell galaxies similar to NGC 7600 in the cold dark matter cosmogony, Star Stream Survey Images By Ken Crawford and be sure to check out the zoomable Full Size Image of NGC 7600 done by Ken Crawford. We thank you all so much for sharing your work with us!

Posted on by Tammy Plotner

Early Galaxy Chemistry: VLT Observes Gamma-Ray Burst

Artist’s impression of a gamma-ray burst shining through two young galaxies in the early Universe. Credit: ESO

[/caption]

“Shot through the heart and you’re to blame…” There’s nothing more powerful than a gamma-ray burst. These abrupt, mega-bright events are captured by orbiting telescopes where the information is immediately relayed to the ground for observation in visible light and infra-red. Some events are so powerful that they linger for hours or even days. But just how quick can we spot them? A burst cataloged as GRB 090323 was picked up by the NASA Fermi Gamma-ray Space Telescope, then confirmed by the X-ray detector on NASA’s Swift satellite and with the GROND system at the MPG/ESO 2.2-metre telescope in Chile. Within a day it was being studied by ESO’s Very Large Telescope. It was so intense it penetrated its host galaxy and another… heading out on a 12 billion light year journey just to get here.

“When we studied the light from this gamma-ray burst we didn’t know what we might find. It was a surprise that the cool gas in these two galaxies in the early Universe proved to have such an unexpected chemical make-up,” explains Sandra Savaglio (Max-Planck Institute for Extraterrestrial Physics, Garching, Germany), lead author of the paper describing the new results. “These galaxies have more heavy elements than have ever been seen in a galaxy so early in the evolution of the Universe. We didn’t expect the Universe to be so mature, so chemically evolved, so early on.”

As the brilliant beacon passed through the galaxies, the gases performed as a filter, absorbing some wavelengths of light. But the real kicker here is we wouldn’t have even known these galaxies existed if it weren’t for the gamma-ray burst! Because the light was affected, astronomers were able to detect the “composition of the cool gas in these very distant galaxies, and in particular how rich they were in heavy elements.” It had been surmised that early galaxies would have less heavy elements since their stellar populations weren’t old enough to have produced them… But the findings pointed otherwise. These new galaxies were rich in heavy elements and going against what we thought we knew about galactic evolution.

So exactly what does that mean? It would appear these new, young galaxies are forming stars at an incredible rate. To enrich their gases so quickly, it’s possible they are in a merger process. While this isn’t a new concept, it just may support the theory that gamma-ray bursts can be associated with “vigorous massive star formation”. Furthermore, it’s surmised that rapid stellar growth may have simply stopped in the primordial Universe. What’s left that we can observe some 12 billion years later are mere shadows of what once was… like cool dwarf stars and black holes. These two newly discovered galaxies are like finding a hidden stain on the outskirts of the distant Cosmos.

“We were very lucky to observe GRB 090323 when it was still sufficiently bright, so that it was possible to obtain spectacularly detailed observations with the VLT. Gamma-ray bursts only stay bright for a very short time and getting good quality data is very hard. We hope to observe these galaxies again in the future when we have much more sensitive instruments, they would make perfect targets for the E-ELT,” concludes Savaglio.

Original Story Source: ESO Press Release. For Further Reading: Super-solar Metal Abundances in Two Galaxies at z ~ 3.57 revealed by the GRB 090323 Afterglow Spectrum.

Posted on by Tammy Plotner

Determining The Galaxy Collision Rate

Galactic Wrecks Far from Earth: These images from NASA's Hubble Space Telescope's ACS in 2004 and 2005 show four examples of interacting galaxies far away from Earth. The galaxies, beginning at far left, are shown at various stages of the merger process. The top row displays merging galaxies found in different regions of a large survey known as the AEGIS. More detailed views are in the bottom row of images. (Credit: NASA; ESA; J. Lotz, STScI; M. Davis, University of California, Berkeley; and A. Koekemoer, STScI)

[/caption]

Big galaxies… Little galaxies… But how often do they meet? Thanks to information from some of the latest Hubble surveys, astronomers have been able to more closely estimate galaxy collision rates than ever before. Apparently those that have happened within the last eight to nine billion years have occurred somewhere in-between previous estimates.

When it comes to galaxy evolution, the collision rate is an indicator of how individual galaxies accumulated mass over time. While it’s pretty much a standard measurement, there’s a large margin with no information of how often it might have occurred in the very distant past. By taking a look at in deep-field surveys made by NASA’s Hubble Space Telescope, astronomers were able to get a general look – one that showed a merger rate of anywhere from 5 percent to 25 percent of those studied.

The science team, led by Jennifer Lotz of the Space Telescope Science Institute in Baltimore, Maryland, took a close look at galaxy interactions spaced over vast distances. This allowed the group to essentially study mergers which occurred at different times. What they found was larger galaxies had a merger rate of once every nine billion years, while smaller ones crashed up more often. When taking a look a dwarf galaxies compared to massive ones, the team found it happened three times more often than the rate for large galaxies.

“Having an accurate value for the merger rate is critical because galactic collisions may be a key process that drives galaxy assembly, rapid star formation at early times, and the accretion of gas onto central supermassive black holes at the centers of galaxies,” Lotz explains.

While there were past studies of galaxy mergers done with Hubble information, astronomers used a different method and came up with different results. “These different techniques probe mergers at different ‘snapshots’ in time along the merger process,” Lotz says. “It is a little bit like trying to count car crashes by taking snapshots. If you look for cars on a collision course, you will only see a few of them. If you count up the number of wrecked cars you see afterwards, you will see many more. Studies that looked for close pairs of galaxies that appeared ready to collide gave much lower numbers of mergers than those that searched for galaxies with disturbed shapes, evidence that they’re in smashups.”

To help determine how often the merger rate occurred with time, Lotz and her team had to know how long an encountered galaxy would appear disrupted. In order to get a good working model, the team used computer simulations and then mapped them compared to Hubble images of galaxy interactions. While this effort took a great deal of time, the team did their best to create every possible scenario – from a pair of galaxies with equal mass to disparate ones. They also took into account orbits, collisional events and even orientation. Of these studies, 57 different situations and 10 viewing angles were accounted for. “Viewing the simulations was akin to watching a slow-motion car crash,” Lotz says. These computer created scenarios followed the galaxies for 2 billion to 3 billion years, starting at the merger beginning and ending a billion years later when completed. “Our simulations offer a realistic picture of mergers between galaxies,” explains Lotz.

While it was easy enough to see what happens with a giant galaxy, it was a bit more difficult to observe what happens with diminutive ones. Observing a dwarf merger is far more difficult simply because they are so much more dim – but plentiful. “Dwarf galaxies are the most common galaxy in the universe,” Lotz says. “They may have contributed to the buildup of large galaxies. In fact, our own Milky Way galaxy had several such mergers with small galaxies in its recent past, which helped to build up the outer regions of its halo. This study provides the first quantitative understanding of how the number of galaxies disturbed by these minor mergers changed with time.”

However, studies of this type just don’t happen with a handful of photos. Lotz and the team had to compare the simulations with literally thousands of galaxy images taken from some of Hubble’s largest surveys, including the All-Wavelength Extended Groth Strip International Survey (AEGIS), the Cosmological Evolution Survey (COSMOS), and the Great Observatories Origins Deep Survey (GOODS), as well as mergers identified by the DEEP2 survey with the W.M. Keck Observatory in Hawaii. At the beginning they found a wide variety of merger rates, but ended up with about a thousand merger candidates. “When we applied what we learned from the simulations to the Hubble surveys in our study, we derived much more consistent results,” Lotz says.

What’s next for Lotz and her team? It’s time to take a look at galaxy interactions that happened about 11 billion years ago. Their goal is to check out when star formation across the Universe reached its greatest as compared to the merger rate. Perhaps there might be a correlation between encounters and rapid star birth!

Original Story Source: Hubble Space Telescope News.