The Leo Triplet. Credit: ESO/INAF-VST/OmegaCAM. Acknowledgement: OmegaCen/Astro-WISE/Kapteyn Institute
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Here’s a brand new, magnificent look at the Leo Triplet — a group of interacting galaxies about 35 million light-years from Earth. This wide field of view comes courtesy of the VLT Survey Telescope (VST) at the Paranal Observatory. It has a field of view twice as broad as the full Moon — which is unusual for a big telescope – and the FOV is wide enough to frame all three members of the group in a single picture. But there’s also a great new view of galaxies in the background, as the VST also brings to light large numbers of fainter and more distant galaxies, some through the wonders of microlensing.
Microlensing is a gravitational lensing phenomenon where the presence of a dim but massive object can be inferred from the effect of its gravity on light coming from a more distant star. If, due to a chance alignment, the dim object passes sufficiently close to our line of sight to the more distant star, its gravitational field bends the light coming from the background star. This can lead to a measurable increase in the background star’s brightness. As microlensing events rely on rare chance alignments, they are usually found by large surveys that can observe great numbers of potential background stars.
One of the science goals of the VST is to search for much fainter objects in the Milky Way, such as brown dwarf stars, planets, neutron stars and black holes, and microlensing is helpful in finding these elusive objects.
All three of the big, main galaxies seen here are spirals like our own Milky Way galaxy, even though this may not be immediately obvious in this image because their discs are tilted at different angles to our line of sight. NGC 3628, left, is seen edge-on, while the Messier objects M 65 (upper right) and M 66 (lower right), on the other hand, are inclined enough to make their spiral arms visible.
Get more information and see a larger version of this image at the ESO website.
One of the strangest types of galaxies are those known as ring galaxies. Examples of these include Hoag’s Object (shown above), the Cartwheel Galaxy, and AM 0644-741. These unusual shapes are cause by a galactic collision in which a smaller galaxy plunges nearly straight through the center of a larger galaxy. The gravitational disturbance caused a wave of star formation to ripple out from the center. In most cases, the intruder galaxy is long gone, but a serendipitous discovery as part of a larger survey recently turned up another of these objects, this time with the collisional partner still making its getaway.
Prior to this discovery, astronomers recognized only 127 ring galaxies, most of which are in the relatively nearby universe (< 1 billion lightyears). The lifetime of the ring structure is generally short lived and will dissipate once the density wave leaves the galaxy but while it persists, such galaxies give astronomers a wonderful chance to study the star formation the process triggers. In particular, it helps astronomers understand stellar evolution since the age of the stars becomes linked to the radius from the center; the newest stars are the furthest out where the ring is currently condensing new ones from the interstellar medium, and older ones lie towards the center where the density wave began.
The new ring galaxy was discovered by astronomers from the Max Planck Institute for Astronomy in Germany as part of a study to explore the Milky Way’s thick disk. The discovery images were taken in 2007 using the recently damaged Subaru telescope.
Auriga's Wheel as seen in the g (left) and r (right) filters from Subaru. Credit: Blair Conn et al.
When the team noticed the rare galaxy in their image they tentatively dubbed it “Auriga’s Wheel”, they turned to the Gemini North telescope to obtain spectroscopy for the object. The redshift of these objects would allow astronomers to explore their distance and confirm that they were likely interacting and not simply a chance alignment. When the data was analyzed, the galaxies were found to lie together at a distance of nearly 1.5 billion lightyears making this a new record holder for furthest ring galaxy for which spectroscopic data has been obtained.
But aside from the temporary place in the record books, the pair is interesting in other ways. Modeling of the interaction as well as the spectroscopic data allowed the team to estimate the propagation of the ring to be at ~200 km/sec which would make it 50 million years since the collision occurred. The image also clearly shows the galaxy that plunged through the center of the more massive, disk galaxy and a distinct trail of gas and dust connects the two. Additionally, both galaxies appear to have Active Galactic Nuclei, which is rare for ring galaxies. However, it is not clear whether the activity was a result of the collision or a property of the individual galaxies prior to the interaction.
IC 342's dust structures show up vividly in red, in this infrared view from Spitzer. Image credit: NASA/JPL-Caltech
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Look, he’s crawling up my wall… Black and hairy, very small… Now he’s up above my head… Hanging by a little thread. Nope. It’s not Boris the Spider, it’s spiral galaxy IC 342 and it’s hanging out in the constellation of Camelopardalis. Thanks to NASA’s Spitzer Space Telescope, we’re able to peer through the dust clouds and sneak a peek at this arachnid appearing beastie.
Residing at an approximate distance of 10 million light-years, this impressive grand design spiral is difficult for details because it’s located directly behind the disk of the Milky Way from our point of view. Tiny particles of interstellar dust, which measure just a fraction of a micron across, approximate the blue wavelength of light. These vast areas composed of silicates, carbon, ice, and/or iron compounds dim the light in a process called extinction – but using infrared vision can even the score. Line-of-sight stars from our galaxy appear blue/white and the blue haze around the galaxy’s nucleus is from IC 342’s collective starlight. Its gangly arms glow a soft crimson and clumps of newly forming stars radiate red.
It’s small wonder the core of IC 342 appears so spooky. According to research, it has undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way. Can you observe Boris yourself? Absolutely. You’ll find this magnitude 9 critter located along the galactic equator at RA 03h 46m 48.5s – Dec +68 05′ 46″. But beware… Its low surface brightness means you’ll need a rich field telescope and good, dark skies.
The galaxy NGC 5557 clearly exhibits extremely extended and faint tidal streams spanning more than 1.2 million light-years from left to right on this image from the MegaCam mounted on the Canada-France-Hawaii Telescope. Image by P.-A. Duc 2011 (c) CEA/CFHT
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Thanks to images taken with the MegaCam camera mounted on the Canada-France-Hawaii Telescope (CFHT, CNRC/CNRS/University of Hawaii), researchers are beginning to see that elliptical galaxies just aren’t acting their age. Their initial studies are showing signs of recent merging – meaning that many could be as much as five times younger than previously thought.
We’ve been studying massive elliptical galaxies for a long time and their stripped down stellar population has always led astronomers to assume most were in the 7 to 10 billion year old age bracket. However, astronomers from CNRS, CEA, CFHT, and the Observatoire de Lyon – all members of the Atlas3D international collaboration – have been sneaking a peak at the galactic fountain of youth. According to observations done on two elliptical galaxies (NGC 680 & NGC 5557), it would appear they’ve undergone a spiral galaxy merger… one that’s happened as recently as 1 to 3 billion years ago.
“Such age estimate is based on the presence of ultra faint filaments in the distant outskirts of the galaxies. These features called tidal streams in the astronomers parlance are typical residuals from a galaxy merger.” says the CFH team. “They are known not to survive in this shape and brightness for more than a few billion years, hence the new age estimate of the resulting elliptical galaxies. These structures were detected for the first time thanks to a very-deep imaging technique boosting the capabilities of CFHT’s wide-field optical imager MegaCam.”
A sample of elliptical galaxies from the Atlas3D survey current collection, all showing clear signs of a recent collision. Image by P.-A. Duc 2011 (c) CEA/CFHT
The Atlas3D team isn’t stopping with these results and they’re looking at a survey of more than one hundred elliptical galaxies close to the Milky Way. When the samples are gathered and compared, they’ll look for more faint extended features that could spell a recent merger. It could mean we need to rethink our standard model for elliptical galaxies formation!
A new study found an excess of counter-clockwise rotating or "left-handed" spiral galaxies like this one, compared to their right-handed counterparts. This provides evidence that the universe does not have mirror symmetry. Credit: NASA, ESA
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It’s called mirror symmetry and it has everything to do with a recent study done by physics professor Michael Longo and a team of five undergraduates from the University of Michigan. Their work encompasses the rotation direction of tens of thousands of spiral galaxies cataloged by the Sloan Digital Sky Survey. What they’re looking for is the shape of the Big Bang… and what they found is much more elaborate than they thought.
By utilizing SDSS images, the team began looking for mirror symmetry and evidence the early universe spun on an axis. “The mirror image of a counter-clockwise rotating galaxy would have clockwise rotation. More of one type than the other would be evidence for a breakdown of symmetry, or, in physics speak, a parity violation on cosmic scales.” Longo said. However, there seems to be a certain “spin preference” when it comes to spiral galaxies toward the north pole of the Milky Way. Here they found an abundance of left-handed, or counter-clockwise rotating, spirals – an effect which extended beyond an additional 600 million light years.
“The excess is small, about 7 percent, but the chance that it could be a cosmic accident is something like one in a million,” Longo said. “These results are extremely important because they appear to contradict the almost universally accepted notion that on sufficiently large scales the universe is isotropic, with no special direction.”
On the other hand, be it left or right, Galaxy Zoo has done some very interesting research into mirror symmetry as well. In conjunction with the Sloan Digital Sky Survey, the team also involved the public for their input – a total of 36 million classifications for 893,212 galaxies from 85,276 users. The GZ study is absolutely fascinating and took every variable into account.
“We wish to establish the large scale statistical properties of the galaxy spins. Although there is some level of uncertainty in the overall number counts, it is still possible to look for a dipole, for example, in the spin distributions.” says Kate Land, et al. “Curiously, the dipoles from these two analyses are in completely opposite directions. The samples cover different amounts and parts of the sky, with SDSS mainly in the Northern hemisphere and the sample of Sugai & Iye (1995) predominantly in the Southern hemisphere. In both cases the dipoles tend to point away from the majority of the data but neither analysis fits for a monopole or takes account of their partial sky coverage in assessing the dipole. With incomplete sky coverage the spherical harmonic decomposition is no longer orthogonal and for a sample covering less than half of the sky it is hard to tell the difference between a monopole (an excess of one type over the other) and a dipole (an asymmetry in the distribution).”
So what’s the end result? Well, chances are good that our universe was born spinning… but like any family, there isn’t much evidence one way or another that says most members have to be right – or left – handed. It’s more about how we, as humans, perceive them…
[/caption]The traditional picture of galaxy growth is not pretty. In fact, it’s a kind of cosmic cannibalism: two galaxies are caught in ominous tango, eventually melding together in a fiery collision, thus spurring on an intense but short-lived bout of star formation. Now, new research suggests that most galaxies in the early Universe increased their stellar populations in a considerably less violent way, simply by burning through their own gas over long periods of time.
The research was conducted by a group of astronomers at NASA’s Spitzer Science Center in Pasadena, California. The team used the Spitzer Space Telescope to peer at 70 distant galaxies that flourished when the Universe was only 1-2 billion years old. The spectra of 70% of these galaxies showed an abundance of H alpha, an excited form of hydrogen gas that is prevalent in busy star-forming regions. Today, only one out of every thousand galaxies carries such an abundance of H alpha; in fact, the team estimates that star formation in the early Universe outpaced that of today by a factor of 100!
This split view shows how a normal spiral galaxy around our local universe (left) might have looked back in the distant universe, when astronomers think galaxies would have been filled with larger populations of hot, bright stars (right). Image credit: NASA/JPL-Caltech/STScI
Not only did these early galaxies crank out stars much faster than their modern-day counterparts, but they created much larger stars as well. By grazing on their own stores of gas, galaxies from this epoch routinely formed stars up to 100 solar masses in size.
These impressive bouts of star formation occurred over the course of hundreds of millions of years. The extremely long time scales involved suggest that while they probably played a minor role, galaxy mergers were not the main precursor to star formation in the Universe’s younger years. “This type of galactic cannibalism was rare,” said Ranga-Ram Chary, a member of the team. “Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought.” Even on cosmic scales, it would seem that slow and steady really does win the race.
As we’ve recently learned, the ATLAS3D project was able to study 260 individual galaxies and do some very amazing things. By imaging in both red and blue shift, astronomers were able to take stellar measurements and give us a clear picture of galaxy rotation. But looking at a computer generated image gives a picture just like you reading the text in this article – no dimension. By superimposing the velocity of the stars over the plane of the image, a new breakthrough in simulation can be made. And it’s coming straight on for you… Continue reading “3D Galaxies – Coming Straight On For You”
Thousands of galaxies observed by the Herschel Space Observatory through the Lockman hole. Credit: ESA.
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You’ve probably heard of the cosmic microwave background, but it doesn’t stop there. The as-yet-undetectable cosmic neutrino background is out there waiting to give us a view into the first seconds after the Big Bang. Then, looking further forward, there are other backgrounds across the electromagnetic spectrum – all of which contribute to what’s called the extragalactic background light, or EBL.
The EBL is the integrated whole of all light that has ever been radiated by all galaxies across all of time. At least, all of time since stars and galaxies first came into being – which was after the dark ages that followed the release of the cosmic microwave background.
The cosmic microwave background was released around 380,000 years after the Big Bang. The dark ages may have then persisted for another 750 million years, until the first stars and the first galaxies formed.
In the current era, the cosmic microwave background is estimated to make up about sixty percent of the photon density of all background radiation in the visible universe – the remaining forty per cent representing the EBL, that is the radiation contributed by all the stars and galaxies that have appeared since.
This gives some indication of the enormous burst of light that the cosmic microwave background represented, although it has since been red-shifted into almost invisibility over the subsequent 13.7 billion years. The EBL is dominated by optical and infrared backgrounds, the former being starlight and the latter being dust heated by that starlight which emits infrared radiation.
Just like the cosmic microwave background can tell us something about the evolution of the earlier universe, the cosmic infrared background can tell us something about the subsequent evolution of the universe – particularly about the formation of the first galaxies.
The power density of the universe's background radiation plotted over wavelength. The cosmic microwave background, though substantially red-shifted due to its age, still dominates. The remainder, extragalactic background light, is dominated by optical and infrared radiation, which have power densities several orders of magnitude higher than the remaining radiation wavelengths.
The Photodetector Array Camera and Spectrometer (PACS) Evolutionary Probe is a ‘guaranteed time’ project for the Herschel Space Observatory. Guaranteed means there always a certain amount of telescope time dedicated to this project regardless of other priorities. The PACS Evolutionary Probe project, or just PEP, aims to survey the cosmic infrared background in the relatively dust free regions of the sky that include: the Lockman Hole; the Great Observatories Origins Deep Survey (GOODS) fields; and the Cosmic Evolution Survey (COSMOS) field.
The Herschel PEP project is collecting data to enable determination of rest frame radiation of galaxies out to a redshift of about z =3, where you are observing galaxies when the universe was about 3 billion years old. Rest frame radiation means making an estimation of the nature of the radiation emitted by those early galaxies before their radiation was red-shifted by the intervening expansion of the universe.
The data indicate that infrared contributes around half of the total extragalactic background light. But if you just look at the current era of the local universe, infrared only contributes one third. This suggests that more infrared radiation was produced in the distant past, than in the present era.
This may be because earlier galaxies had more dust – while modern galaxies have less. For example, elliptical galaxies have almost no dust and radiate almost no infrared. However, luminous infrared galaxies (LIRGs) radiate strongly in infrared and less so in optical, presumably because they have a high dust content.
Modern era LIRGs may result from galactic mergers which provide a new supply of unbound dust to a galaxy, stimulating new star formation. Nonetheless, these may be roughly analogous to what galaxies in the early universe looked like.
Dustless, elliptical galaxies are probably the evolutionary end-point of an galactic merger, but in the absence of any new material to feed off these galaxies just contain aging stars.
So it seems that having a growing number of elliptical galaxies in your backyard is a sign that you live in a universe that is losing its fresh, infrared flush of youth.
Abell 2744, shown above in a composite of images from the Hubble Space Telescope, the ESO’s Very Large Telescope and NASA’s Chandra X-ray Observatory, is one of the most complex and dramatic collisions ever seen between galaxy clusters.
X-ray image of Abell 2744
Dubbed “Pandora’s Cluster”, this is a region 5.9 million light-years across located 3.5 billion light-years away. Many different kinds of structures are found here, shown in the image as different colors. Data from Chandra are colored red, showing gas with temperatures in the millions of degrees. Dark matter is shown in blue based on data from Hubble, the European Southern Observatory’s VLT array and Japan’s Subaru telescope. Finally the optical images showing the individual galaxies have been added.
Even though there are many bright galaxies visible in the image, most of the mass in Pandora’s Cluster comes from the vast areas of dark matter and extremely hot gas. Researchers made the normally invisible dark matter “visible” by identifying its gravitational effects on light from distant galaxies. By carefully measuring the distortions in the light a map of the dark matter’s mass could be created.
Galaxy clusters are the largest known gravitationally-bound structures in the Universe, and Abell 2744 is where at least four clusters have collided together. The vast collision seems to have separated the gas from the dark matter and the galaxies themselves, creating strange effects which have never been seen together before. By studying the history of events like this astronomers hope to learn more about how dark matter behaves and how the different structures that make up the Universe interact with each other.
Check out this HD video tour of Pandora’s Cluster from the team at Chandra:
Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!
Bluer galaxies are actively “awake” and forming stars, while redder galaxies have shut down and are “asleep.” (Image: NASA, ESA, S. Beckwith (STScI) and the HUDF team)
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It’s a well known fact that galaxies come in two types – either actively forming stars or not. In simplistic terms, that means they are either awake or asleep. But now scientists are looking back twelve billion light years across time to find the same holds just as true then as it does now. As a matter of fact, galaxies may have been behaving this way for around 85% of the history of the Universe.
“The fact that we see such young galaxies in the distant universe that have already shut off is remarkable,” said Kate Whitaker, a Yale University graduate student and lead author of the paper, which is published in the June 20 online edition of the Astrophysical Journal.
So, without poking the sleeping dragon, just how did the astronomers make their determinations? Try with the use of a 4-meter Kitt Peak telescope in Arizona and a special set of filters developed by Whitaker and her team. Just like all astronomy filters, this new breed is selective to certain bandpasses, or wavelengths, of light. These new filter sets were then used on 40,000 galaxies over a 75 night period and the data collected and examined. The end product was the deepest and most comprehensive of its kind so far. Active, awake galaxies appear more blue, while the sleepy-heads appear red. Believe it or not, when it comes to the cosmic bedroom there’s more activity than previously thought.
“We don’t see many galaxies in the in-between state,” said Pieter van Dokkum, a Yale astronomer and another author of the paper. “This discovery shows how quickly galaxies go from one state to the other, from actively forming stars to shutting off.”
Whether the dozing galaxies have completely shut down remains an open question, Whitaker said. However, the new study suggests the active galaxies are forming stars at rates about 50 times greater than their somnambulistic counterparts. “Next, we hope to determine whether galaxies go back and forth between waking and sleeping or whether they fall asleep and never wake up again,” van Dokkum said. “We’re also interested in how long it takes galaxies to fall asleep, and whether we can catch one in the act of dozing off.”
Pass the Red Bull… and sing the blues! “Are you sleeping? Can you hear me? Do you know if I am by your side? Does it matter? If you hear me? When the mornin’ comes I’ll be there by your side… There was a time, we had a time. There was a time we had time…”
