galaxies Archives

January 29, 2010December 24, 2015 by Jean Tate

Death in the Sky: M31 Shreds its Satellites

False-color map of the density of red giants in M31 (Star count map credit: Mikito Tanaka, Tohoku University)

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An international team of astronomers has identified two new tidal streams in M31, the Andromeda galaxy. They are more-or-less intact remnants of dwarf galaxies that M31 has otherwise ripped to shreds.

One team – using the Suprime-Cam camera on Subaru – discovered two new dwarf galaxy shards by mapping the sky density of red giants in M31’s outskirts; the other – using the DEIMOS spectrograph on Keck II – separated the M31 red giant wheat from the Milky Way chaff.

In a project led by collaborators Mikito Tanaka and Masashi Chiba of Tohoku University, Japan, the astronomers used the Subaru 8-meter telescope and Suprime-Cam camera to map the density of red giants in large portions of M31, including the hitherto uncharted north side. This led to the discovery of two tidal streams to the northwest (streams E and F) at projected distances of 60 and 100 kiloparsecs (200,000 and 300,000 light-years) from M31’s nucleus. The study also confirmed a few previously known streams, including the little-studied diffuse stream to the southwest (stream SW), which lies at a projected distance of 60 to 100 kiloparsecs (200,000 to 300,000 light years) from M31’s nucleus.

The Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo (SPLASH) collaboration, a large survey of red giants in M31 lead by Puragra Guhathakurta, professor of astronomy and astrophysics at the University of California, Santa Cruz, has followed up with a spectroscopic survey of several hundred red giants in Streams E, F, and SW, using the Keck II 10-meter telescope and DEIMOS spectrograph at the W. M. Keck Observatory in Hawaii. Analysis of the spectra from this survey yields estimates of the line-of-sight velocity of the stars, which in turn allows M31 red giants to be distinguished from foreground stars (in the Milky Way). The spectral data confirmed the presence of coherent groups of M31 red giants moving with a common velocity.

Distribution of line-of-sight velocities in the Stream SW field (Raja Guhathakurta)

Stars spread over the vast reaches of a halo in a big galaxy like the Milky Way or M31 are characterized by old age, few elements other than helium and hydrogen (i.e. low metallicities; astronomers call all elements other than hydrogen and helium “metals”), and high velocities. The exceptional nature of these halo stars, when compared to stars in a galaxy’s disk, reflects the early dynamics and element formation of the galaxy when its appearance differed significantly from what we see today. Consequently, the halo provides important insights into the processes involved in the formation and evolution of a massive galaxy. In the best Big Bang model we have today – ΛCDM (Lambda Cold Dark Matter) – the outer halos are built up through the merger and dissolution of smaller, dwarf, satellite galaxies. “This process of galactic cannibalism is an integral part of the growth of galaxies,” said Guhathakurta.

The smooth, well-mixed population of halo stars in these large galaxies represents the aggregate of the dwarf galaxy victims of this cannibalism process, while the dwarf galaxies that are still intact as they orbit their large parent galaxy are the survivors of this process.

“The merging and dissolution of a dwarf galaxy typically lasts for a couple billion years, so one occasionally catches a large galaxy in the act of cannibalizing one of its dwarf galaxy satellites,” Guhathakurta said. “The characteristic signature of such an event is a tidal stream: an enhancement in the density of stars, localized in space and moving as a coherent group through the parent galaxy.”

Tidal streams are important because they represent a link between the victims and survivors of galactic cannibalism – an intermediate stage between the population of intact dwarf galaxies and the well-mixed stars dissolved in the halo.

The Andromeda galaxy is a unique test bed for studying the formation and evolution of a large galaxy, said Guhathakurta, “Our external vantage point gives us a global perspective of the galaxy, and yet the galaxy is close enough for us to obtain detailed measurements of individual red giant stars within it.”

One of the next steps will be to measure the detailed elemental compositions (“chemical properties”, in astronomer-speak) of red giants in these newly discovered tidal streams in M31. Comparing the chemical properties of tidal streams, intact dwarf satellites, and the smooth halo will be of particular significance, Guhathakurta said. Mikito Tanaka put it this way: “Further observational surveys of an entire halo region in Andromeda will provide very useful information on galaxy formation, including how many and how massive individual dwarf galaxies as building blocks are and how star formation and chemical evolution proceeded in each dwarf galaxy.”

At the present time, detailed studies of the chemical properties of tidal streams, intact dwarf satellites, and smooth stellar halos are possible only in the Milky Way and M31 galaxies and their immediate surroundings. Existing telescopes and instruments are simply not powerful enough for astronomers to carry out such studies in more distant galaxies. This situation will improve greatly with the advent of the planned Thirty Meter Telescope later in this decade, Guhathakurta said.

Tanaka’s team published their survey results in a recent Astrophysics Journal (ApJ) paper (the preprint is arXiv:0908.0245), and Guhathakurta’s team presented their results on the newly discovered tidal streams earlier this month at the 215th meeting of the American Astronomical Society in Washington, D.C.; they hope to have an ApJ paper on these results published later this year. You can read an earlier SPLASH paper, “The SPLASH Survey: A Spectroscopic Portrait of Andromeda’s Giant Southern Stream”, published in ApJ (the preprint is arxiv:0909.4540).

Sources: University of California, Santa Cruz, National Astronomical Observatory of Japan.

January 14, 2010December 24, 2015 by Nancy Atkinson

Latest from Hubble: Star Formation Fizzling Out in Nearby Galaxy

NGC 2976.. NASA, ESA, and J. Dalcanton and B. Williams (University of Washington, Seattle)

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Most galaxies are throughout the universe are happenin’ places, with all sorts of raucous star formation going on. But for a nearby, small spiral galaxy, the star-making party is almost over. In this latest Hubble release, astronomers were surprised to find that star-formation activities in the outer regions of NGC 2976 are fizzling out, and any celebrating is confined to a few die-hard partygoers huddled in the galaxy’s inner region.

The reason? Well, the star birth began when another party-crashing galaxy interacted with NGC 2976. But that happened long ago, and now star formation in the galaxy is fizzling out in the outer parts as some of the gas was stripped away and the rest collapsed toward the center. With no gas left to fuel the party, more and more regions of the galaxy are going to sleep.

“Astronomers thought that grazing encounters between galaxies can cause the funneling of gas into a galaxy’s core, but these Hubble observations provide the clearest view of this phenomenon,” explains astronomer Benjamin Williams of the University of Washington in Seattle, who directed the Hubble study, which is part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. “We are catching this galaxy at a very interesting time. Another 500 million years and the party will be over.”

NGC 2976 does not look like a typical spiral galaxy. It has a star-forming disk, but no obvious spiral pattern. Its gas is centrally concentrated, but it does not have a central bulge of stars. The galaxy resides on the fringe of the M81 group of galaxies, located about 12 million light-years away in the constellation Ursa Major.

“The galaxy looks weird because an interaction with the M81 group about a billion years ago stripped some gas from the outer parts of the galaxy, forcing the rest of the gas to rush toward the galaxy’s center, where it is has little organized spiral structure,” Williams says.

The galaxy’s relatively close distance to Earth allowed Hubble’s Advanced Camera for Surveys (ACS) to resolve hundreds of thousands of individual stars. What look like grains of sand in the image are actually individual stars. Studying the individual stars allowed astronomers to determine their color and brightness, which provided information about when they formed.

The image was taken over a period in late 2006 and early 2007.

“This type of observation is unique to Hubble,” Williams says. “If we had not been able to pick out individual stars, we would have known that the galaxy is weird, but we would not have dug up evidence for a significant gas rearrangement in the galaxy, which caused the stellar birth zone to shrink toward the galaxy’s center.”

Simulations predict that the same “gas-funneling” mechanism may trigger starbursts in the central regions of other dwarf galaxies that interact with larger neighbors. The trick to studying the effects of this process in detail, Williams says, is being able to resolve many individual stars in galaxies to create an accurate picture of their evolution.

Williams’ results will appear in the January 20, 2010 issue of The Astrophysical Journal.

Source: HubbleSite

January 12, 2010December 24, 2015 by Nancy Atkinson

Dark Energy Model Explains ‘Hubble Sequence’ of Galaxies

A figure illustrating the Hubble sequence. On the left are elliptical galaxies, with their shapes ranging from spherical (E0) to elongated (E7). Type S0 is intermediate between elliptical and spiral galaxies. The upper right line of objects stretch from Sa (tightly wound spiral) to Sc (loosely wound spiral). The lower right line shows the barred spirals that range from the tightly wound SBa to loosely wound SBc types. Image: Ville Koistinen

Caption: A figure illustrating the Hubble sequence. Image: Ville Koistinen

One look at a Hubble Deep Field image reveals that galaxies come in all sorts of shapes and sizes. But why? Astronomers have been at a loss to explain the diversity of galaxy shapes seen in the Universe. But now, two astronomers have tracked the evolution of galaxies over thirteen billion years from the early Universe to the present day, helping to clarify the “Hubble Sequence,” a classification of galaxies developed by Edwin Hubble. Keys to their model include galaxy mergers and dark energy.

Dr. Andrew Benson of Caltech and Dr. Nick Devereux of Embry-Riddle University in Arizona Benson and Devereux combined data from the infrared Two Micron All Sky Survey (2MASS) with sophisticated computer model they developed, called GALFORM. The model reproduced the evolutionary history of the Universe over thirteen billion years. To their surprise, their computations reproduced not only the different galaxy shapes but also their relative numbers.

Caption: The image shows some of the galaxies generated by the computer model. The yellow objects are most distant and therefore appear as they were 13 billion years ago, whilst those closer are seen as they looked more recently. Image: A. Benson (University of Durham), NASA / STScI

“We were completely astonished that our model predicted both the abundance and diversity of galaxy types so precisely,” said Devereux. “It really boosts my confidence in the model,” Benson said.

The astronomers’ model is underpinned by and endorses the ‘Lambda Cold Dark Matter’ model of the Universe. Here ‘Lambda’ is the mysterious ‘dark energy’ component believed to make up about 72% of the cosmos, with cold dark matter making up another 23%. Just 4% of the Universe consists of the familiar visible or ‘baryonic’ matter that makes up the stars and planets of which galaxies are comprised.

Galaxies are thought to be embedded in very large haloes of dark matter and Benson and Devereux believe these to be crucial to their evolution. Their model suggests that the number of mergers between these haloes and their galaxies drives the final outcome – elliptical galaxies result from multiple mergers whereas disk galaxies have seen none at all. Our Milky Way galaxy’s barred spiral shape suggests it has seen a complex evolutionary history, with only a few minor collisions and at least one episode where the inner disk collapsed to form the large central bar.

In Hubble’s classification, there are three basic shapes: spiral, where arms of material wind out in a disk from a small central bulge; barred spiral, where the arms wind out in a disk from a larger bar of material; and elliptical, where the galaxy’s stars are distributed more evenly in a bulge without arms or disk. The different types clearly result from different evolutionary paths, which Benson and Devereux’s model now explains.

“These new findings set a clear direction for future research. Our goal now is to compare the model predictions with observations of more distant galaxies seen in images obtained with the Hubble and those of the soon to be launched James Webb Space Telescope (JWST)”, said Devereux.

Their results appear in the journal Monthly Notices of the Royal Astronomical Society.

Benson and Devereux’s paper.

Lead image complete caption: A figure illustrating the Hubble sequence. On the left are elliptical galaxies, with their shapes ranging from spherical (E0) to elongated (E7). Type S0 is intermediate between elliptical and spiral galaxies. The upper right line of objects stretch from Sa (tightly wound spiral) to Sc (loosely wound spiral). The lower right line shows the barred spirals that range from the tightly wound SBa to loosely wound SBc types. Image: Ville Koistinen

Source: RAS

December 29, 2009December 24, 2015 by Jon Voisey

Galactic Building Blocks

The current view of galactic formation is that galaxies form from a “bottom-up” method. In this picture, small dwarf galaxies, full of metal poor stars, were attracted by dark matter halos in the early universe which merged into larger galaxies. Many of those metal poor stars can still be seen today in the halo of the galaxy, but it was thought that the building blocks from which the galaxies were constructed were long gone or had evolved on their own and would no longer resemble the primordial building blocks.

However, earlier this year, an extremely metal poor star with only 0.00025% of the iron in the Sun was discovered in the Sculptor dwarf galaxy. If confirmed, this would show a strong link to further support the notion that metal poor dwarf galaxies were related to the metal poor stars that still populate our halo. Confirming this was the subject of a recent paper.

For their study, the authors analyzed the newly discovered star (S1020549) with a high resolution spectrograph. From this, they confirmed that the star had very little iron present (an element generally used as an indicator of overall heavy element abundance since its absorption lines feature prominently in the spectra and are easily detectable). The extremely low ratio of iron to hydrogen makes it currently the most metal poor star known in a dwarf galaxy (the overall record holder for metal deficiency is HE 1327–2327).

The study determined an overall [Fe/H] abundance of -3.8 (see how this abundance is defined here) which is very similar to the [Fe/H] abundance of archetypical halo stars of about -4.0. Furthermore, many of the other elemental abundances that were uncovered with the detailed spectroscopy (especially those of Mg, Ca, Sc, Ti, and Cr) also fit the general abundance level of stars found in our halo.

This isn’t a conclusive tie between the two and more such stars will need to be uncovered to reinforce the similarities, but since S1020549 was discovered with “a relatively modest survey” this may suggest “that future observational searches should discover more such objects in Sculptor and other dwarf galaxies.”

December 11, 2009December 24, 2015 by Jon Voisey

Spirals, Tides, and M51

Spiral galaxies are undoubtedly one of the most beautiful structures in the universe. Yet, their simple elegance belies a complex nature. How do such structures not “wind up” and what causes them in the first place? The answers to these questions is a long standing challenge. Under one model, spiral structure is created by spiral density waves. In another, they are induced by tidal interactions. It is this approach that is explored in a new paper by Dobbs et al., accepted for publication in the Monthly Notices of the Royal Astronomical Society. Specifically, the authors attempted to use modeling of tidal forces to recreate the structure of the spiral arms on the grand design spiral, M51.

To model the interaction, they began with a model of a simple galaxy with a mass distribution (broken into a disc, bulge, and halo) similar to that for M51. Their initial galaxy was initially free of spiral structure, but “gravitational instabilities in the stars [Note: as opposed to the galactic gas. Not in individual stars.] produce a multi-armed” and patchy spiral structure (known as a flocculent spiral). This flocculent nature was first predicted in a 1964 paper by Toomre and has been simulated numerous times since then. Dobbs’ team then introduced a point source to represent the smaller galaxy (NGC 5195) along the orbital parameters derived by previous simulations of Theis and Spinneker in 2003.

For the first 60 million years, significant new structure was not evidence. The disc showed some perturbation due to the approaching companion, but no new spiral structure arose. However, by 120 million years from the start of the simulation, hints of a spiral arm on the side of the galaxy closest to the companion begin forming and by 180 million years, two pronounced “grand design” spiral arms dominate the face of the galaxy, spanning over 15,000 light years.

But the arms were too good to last. By 240 million years, the arms only stretch to a mere 6,500 light years as the gravitational forces from the companion seem to shepherd the galaxy’s gas as it is pulled around in its orbit. By 300 million years, the spiral arms have grown again and the pair looks remarkably similar to the present state of the M51/NGC 5195 system.

Comparison of simulation at 300 million years to HST image.

The authors note several features their simulation has in common with the observed galaxy. On the side where the companion first approached the galaxy, they note a “kink” in one arm (labeled as A in image to left). Another similarity is a splitting of one of the spiral arms although, again, the exact positioning is different (labeled B).

Another comparison the authors made was to the strengths (or amplitude) of various arm patterns (1 arm, 2 arm, 3 arm, etc…) over time. They found that the two armed pattern was the most predominant, but from the mechanics, they determined there were underlying higher armed structures that never fully took hold. However, these higher armed patterns did come close to the strength of the 2 arm spiral. The authors note that this is consistent with the observational findings of another group studying M51 in a work that has yet to be prepared for publication.

However, there are also some differences. A plume of gas extended from the simulated M51 which has no counterpart in actual observations (labeled C). Actual observations show large amounts of gas in front of the companion galaxy which are not present to the same degree in the simulation (labeled D). Lastly, real observations show a noticeable flattening of M51’s arms closest to the companion. Again, these do not appear in the simulation. The authors suggest discrepancies may be due to the over simplistic modeling of NGC 5195 as a point source instead of an extended body, or slight differences in initial parameters when compared to the actual system.

Even with these differences, the authors suggest that their modeling of the interaction shows that spiral structure, at least in this case, is most likely the result of the tidal interaction on M51 by NGC 5195. They also note that spiral density waves are likely not the culprit since other studies have not been able to determine a consistent “pattern speed” for the galaxy (the pattern speed is the angular speed at which the arms would rotate if viewed as a coherent structure). Instead, observations showed that the arms should have different pattern speeds at different radii.

Although their work does not suggest that all spiral structure is formed by tidal interactions with companions, this work makes a strong case for the possibility in many galaxies which would have such companions and M51 in specific. Furthermore, the simulations also reveal that these tidally induced arms are a temporary phenomenon. Since they do not have a fixed speed, they will slowly wind up and as the interaction progresses, the galaxies will be further distorted and eventually merge.

(Thanks to Claire Dobbs for permission to reproduce images from the paper as well as clarification on a few points.)

December 8, 2009December 24, 2015 by Nancy Atkinson

Hubble Takes a New “Deep Field” Image with Wide Field Camera 3

Hubble’s latest image is another stunner — and just look at all the galaxies! Hubble has produced a new version of the Ultra Deep Field, this time in near-infrared light and taken with the newly installed Wide Field Camera 3. This is the deepest image yet of the Universe in near-infrared, and so the faintest and reddest objects in the image are likely the oldest galaxies ever identified, and they likely formed only 600–900 million years after the Big Bang. This image was taken in the same region as the visible Ultra Deep Field in 2004, but this new deep view at longer wavelengths provides insights into how galaxies grew in their formative years early in the Universe’s history.

“Hubble has now re-visited the Ultra Deep Field which we first studied 5 years ago, taking infrared images which are more sensitive than anything obtained before,” said Dr. Daniel Stark, a postdoctoral researcher from Cambridge University. “We can now look even further back in time, identifying galaxies when the Universe was only 5 percent of its current age – within 1 billion years of the Big Bang.”

A portion of the Hubble Ultra Deep Field showing the location of a potentially very distant galaxy (marked by crosshairs). Credit: Oxford University

The image was taken during a total of four days in August 2009, with 173,000 seconds of total exposure time. Since infrared light is invisible to the human eye and therefore does not have colors that can be perceived, the image is a “natural” representation that in shorter infrared wavelengths are represented as blue and the longer wavelengths as red. The faintest objects are about one billion times fainter than the dimmest visible objects seen with the naked eye.

Click here for a video zooming into the Ultra Deep Field.

“The expansion of the Universe causes the light from very distant galaxies to appear more red, so having a new camera on Hubble which is very sensitive in the infrared means we can identify galaxies at much greater distances than previously possible,” said Stephen Wilkins, from Oxford University.

Where is the new Ultra Deep Field in the sky? Credit: HubbleSite

The team that took this image in August of 2009 have made it available for research by astronomers worldwide, and a multitude of astronomers have been furiously searching through the data for the most distant galaxies yet discovered. In just three months, twelve scientific papers on these new data have been submitted.

As well as identifying potentially the most distant objects yet, these new HST observations present an intriguing puzzle. “We know the gas between galaxies in the Universe was ionized (or fried) early in history, but the total light from these new galaxies may not be sufficient to achieve this,” said Andrew Bunker, from the University of Oxford.

Installation of Wide Field Camera 3 by astronauts as part of servicing mission 4. Courtesy of NASA.

“These new observations from HST are likely to be the most sensitive images Hubble will ever take, but the very distant galaxies we have now discovered will be studied in detail by Hubble’s successor, the James Webb Space Telescope, which will be launched in 2014,” said Professor Jim Dunlop at the University of Edinburgh.

Papers:
1. By R.J. McLure, J.S. Dunlop, M. Cirasuolo, A.M. Koekemoer, E. Sabbi, D.P. Stark, T.A. Targett, R.S. Ellis,

2. By Stephen M. Wilkins, Andrew J. Bunker, Richard S. Ellis, Daniel Stark, Elizabeth R. Stanway, Kuenley Chiu, Silvio Lorenzoni, Matt J. Jarvis

3. By Bunker, Andrew; Wilkins, Stephen; Ellis, Richard; Stark, Daniel; Lorenzoni, Silvio; Chiu, Kuenley; Lacy, Mark; Jarvis, Matt; Hickey, Samantha,

Sources: Oxford University, Space Telescope Center

December 4, 2009December 24, 2015 by Jon Voisey

How Galaxies Lose Their Gas

Galaxy mergers, such as the Mice Galaxies will be part of Galaxy Zoo's newest project. Credit: Hubble Space Telescope — The Mice galaxies, merging. Credit: Hubble Space Telescope

As galaxies evolve, many lose their gas. But how they do this is a point of contention. One possibility is that it is used to form stars when the galaxies undergo intense periods of star formation known as starburst. Another is that when large galaxies collide, the stars pass through one another but the gas gets left behind. It’s also possible that the gas is pulled out in close passes to other galaxies through tidal forces. Yet another possibility involves a wind blowing the gas out as galaxies plunge through the thin intergalactic medium in clusters through a process known as ram pressure.

A new paper lends fresh evidence to one of these hypotheses. In this paper, astronomers from the University of Arizona were interested in galaxies that displayed long gas tails, much like a comet. Earlier studies had found such galaxies, but it was unclear whether or not this gas tail was pulled out from tidal forces, or pushed out from ram pressure.

To help determine the cause of this the team used new observations from Spitzer to look for subtle differences in the causes of a tail following the galaxy ESO 137-001. In cases where tails are known to be pulled out tidally (such as in the M81/M82 system), there “is no physical reason why the gas would be preferentially stripped over stars.” Stars from the galaxy are pulled out as well and often large amounts of new star formation are induced. Meanwhile, ram pressure tails should be largely free of stars although some new star formation may be expected if there is turbulence in the tail which causes regions of higher density (think like the wake of a boat).

Examining the tail spectroscopically, the team was unable to detect the presence of large numbers of stars suggesting tidal processes were not responsible. Furthermore, the disk of the galaxy seemed relatively undisturbed by gravitational interactions. To support this, the team calculated the relative strengths of the forces acting on the galaxy. They found that, between the tidal forces acting on the galaxy from its parent cluster, and its own centripetal forces, the internal forces where greater, which reaffirmed that tidal forces were an unlikely cause for the tail.

But to confirm that ram pressure was truly responsible, the astronomers looked at other parameters. First they estimated the gravitational force for the galaxy. In order to strip the gas, the force generated by the ram pressure would have to exceed the gravitational one. The energy imparted on the gas would then be measurable as a temperature in the gas tail which could be compared to the expected values. When this was observed, they found that the temperature was consistent with what would be necessary for ram stripping.

From this, they also set limits on how long gas could last in such a galaxy. They determined that in such circumstances, the gas would be entirely stripped from a galaxy in ~500 million to 1 billion years. However, because the density of the gas through which the galaxy would slowly become denser as it passed through the more central regions of the cluster, they suggest the timescale would be much simpler. While this timescale say seem long, it is still shorter than the time it takes such galaxies to make a full orbit in their cluster. As such, it is possible that even in one pass, a galaxy may lose its gas.

If the gas loss occurs on such short timescales, this would further predict that tails like the one observed for ESO 137-001 should be rare. The authors note that an “X-ray survey of 25 nearby hot clusters only discovered 2 galaxies with X-ray tails.”

Although this new study in no way rules out other methods of removing a galaxy’s gas, this is one of the first galaxies for which the ram stripping method is conclusively demonstrated.

Source:

A Warm Molecular Hydrogen Tail Due to Ram Pressure Stripping of a Cluster Galaxy

December 1, 2009December 24, 2015 by Nicholos Wethington

Quasar Caught Building Future Home Galaxy

An artist's impression of how quasars may be able to construct their own galaxies. Image Credit: ESO/L. Calcada

The birth of galaxies is quite a complicated affair, and little is known about whether the supermassive black holes at the center of most galaxies formed first, or if the matter in the galaxy accreted first, and formed the black hole later. Observations of the quasar HE0450-2958, which is situated outside of a galaxy, show the quasar aiding a nearby galaxy in the formation of stars. This provides evidence for the idea that supermassive black holes can ‘build’ their own galaxies.

The quasar HE0450-2958 is an odd entity: normally, supermassive black holes – also known as quasars – form at the center of galaxies. But HE0450-2958 doesn’t appear to have any host galaxy out of which it formed. This was a novel discovery in its own right when it was made back in 2005. Here’s our original story on the quasar, Rogue Supermassive Black Hole Has No Galaxy.

The formation of the quasar still remains a mystery, but current theories suggest that it formed out of cold interstellar gas filaments that accreted over time, or was somehow ejected from its host galaxy by a strong gravitational interaction with another galaxy.

The other oddity about the object is its proximity to a companion galaxy, which it may be aiding to form stars. The companion galaxy lies directly in the sights of one of the quasar’s jets, and is forming stars at a frantic rate. A team of astronomers from France, Germany and Belgium studied the quasar and companion galaxy using the Very Large Telescope at the European Southern Observatory. The astronomers were initially looking to find an elusive host galaxy for the quasar.

The phenomenon of ‘naked quasars’ has been reported before, but each time further observations are made, a host galaxy is found for the object. Energy streaming from the quasars can obscure a faint galaxy that is hidden behind dust, so the astronomers used the VLT spectrometer and imager for the mid-infrared (VISIR). Mid-infrared observations readily detect dust clouds. They combined these observations with new images obtained from the Hubble Space Telescope in the near-infrared.

Observations of HE0450-2958, which lies 5 billion light years from Earth, confirmed that the quasar is indeed without a host galaxy, and that the energy and matter streaming out of the jets is pointed right at the companion galaxy. This scenario is ramping up star formation in that galaxy: 340 solar masses of stars a year are formed in the galaxy, one-hundred times more than for a typical galaxy in the Universe. The quasar and the galaxy are close enough that they will eventually merge, finally giving the quasar a home.

David Elbaz of the Service d’Astrophysique, who is the lead author of the paper which appeared in Astronomy & Astrophysics, said “The ‘chicken and egg’ question of whether a galaxy or its black hole comes first is one of the most debated subjects in astrophysics today. Our study suggests that supermassive black holes can trigger the formation of stars, thus ‘building’ their own host galaxies. This link could also explain why galaxies hosting larger black holes have more stars.”

‘Quasar feedback’ could be a potential explanation for how some galaxies form, and naturally the study of other systems is needed to confirm whether this scenario is unique, or a common feature in the Universe.

Source: ESO, Astronomy & Astrophysics

November 23, 2009December 24, 2015 by Nancy Atkinson

Try Your Hand At Galaxy Zoo’s New “Slot Machine”

Here’s your chance to play online slot machines without risking your life savings. Plus it’s an opportunity to contribute to a citizen science project that is sure to revolutionize our understanding of galaxy mergers. Galaxy Zoo’s newest project asks for help in looking at colliding galaxies, and uses a tool akin to a cosmic slot machine to compare images of galactic pile-ups with millions of simulated mergers.

“The analogy I’ve been using is that it is like driving past a car crash,” said Galaxy Zoo team member Chris Lintott from Oxford University. “You get a snapshot of the action, but there are two things you want to know: what caused the crash (or what did things look like before it all went wrong), and you want to know what the outcome is going to be. We’re doing the same thing. We want to know what the galaxies looked like before the mergers started disrupting them, and we want to know how they are going to end up. Just like our other Galaxy Zoo projects, humans are much better at doing this than computers, and lots of humans are even better.”

The Galaxy Zoo mergers project goes live on November 24 at http://mergers.galaxyzoo.org

“This is another classic Galaxy Zoo problem,” Lintott told Universe Today. “We found 3,000 galaxy mergers from Galaxy Zoo 1, and we don’t have a good understanding of the processes that take place during and after the collisions. This new project will help us work that out.”

On the Galaxy Zoo Mergers page, there will be a real image of a galactic merger in the center and with eight randomly selected merger simulations filling the other eight ‘slots’ around it. Visitors to the site pick which animation best demonstrates what is happening in that collision. But if they don’t see a good simulation, they can “spin the wheel again,” Lintott said, until a good depiction of the merger shows up.

A Grazing Encounter Between Two Spiral Galaxies (NGC 2207 and IC2163). Credit: HubbleSite

“By randomly cycling through the millions of simulated possibilities and selecting only the very best matches the users are helping to build up a profile of what kind of factors are necessary to create the galaxies we see in the Universe around us — and, hopefully, having fun too,” Lintott said.

There’s also the “enhance” option, where you can take control. “Once you have picked a simulation, you can take control of it directly, and change the parameters by hand such as the size, mass, the speed, for example. So, if you get impatient you can take control and see if you can do a better job than the slot machine,” Lintott explained.

For some of mergers, there will be a unique solution – only one way to get the merger we see today. For others there may be many different simulations that could provide the answer.

The Mergers project is a bit different than the regular Galaxy Zoo in that there will be, initially, just one daily challenge. “We’re aiming for one a day, but obviously if everyone who reads Universe Today turns up, we’ve got an idea of how many people we need to look at each one, so then we’ll change them out quicker,” Lintott said. “The more that people do, the more galaxies they’ll get to see.”

Of course, galaxy mergers are beautiful and amazing astronomical objects to behold, so the Galaxy Zoo team is hoping this will be a popular project.

“The point of Galaxy Zoo is to try and understand how we got the mix of galaxies that we see today,” Lintott said. “One of the mysteries is trying to work out how the ellipticals formed. We know that one way to form elliptical is to smash two spirals together. There’s the famous simulation of the Milky Way and Andromeda colliding and everyone assumes it will end up as a big elliptical that has used up all its gas. But actually it’s not clear how often that happens, and it’s not clear that you always get elliptical when you smash spirals together. In fact we know that in some cases they don’t. There is a lot of debate as to how important mergers are in this process.”

Right now, 3% of galaxies are in the process of merging, so, Lintott said, if most big galaxies undergo a merger every million years or so, this is clearly an important process.

“But we don’t understand what affects it has, and that’s what we hope to realize in this project.”

And Lintott admitted this newest Galaxy Zoo project is supposed to be fun and addictive. “Some people will love it, and some people will probably prefer the regular Galaxy Zoo. But it’s nice to have a range of scientific tasks that we have to work through.”

For more information:

Galaxy Zoo Mergers

Galaxy Zoo

November 22, 2009December 24, 2015 by Nicholos Wethington

Ring of Stars in Centaurus A Uncovered

Centaurus A (NGC 5128) is one of the most studied objects in the Southern sky, because it is the giant elliptical galaxy with the closest proximity to our own Milky Way. It lies 11 million light years away from the Milky Way, and is believe to have merged with another gaseous galaxy about 200 to 700 million years ago. The result of this galactic mashup: the birth of hundreds of thousands of stars in a kiloparsec-spanning ring near the core.

This is the first time that the inner structure of the galaxy has been resolved in such detail. Using the SOFI large field Infra-Red (1-2.5 micron) spectro-imager at the ESO New Technology Telescope, a research team led by Jouni Kainulainen of the University of Helsinki and Max Planck Institute for Astronomy was able to image a large ring of stars that have formed – and are still continuing to form – near the center of the galaxy. The brightest sources in the ring are red supergiants, or low-mass star clusters.

“It is important to note that it is not decisively the instrument (the telescope or the instrument attached to it) that enables us to see through dust, but the data analysis technique that is used to analyze the images taken with it. Of course, the instrument plays a big role in a sense that adequately high-quality images are needed to perform the analysis,” Dr. Kainulainen said in an email interview.

“There is a fundamental difference between the images we use in our paper and the Spitzer images: the wavelength that the images cover. In the images we used in our work, the dust lane of Centaurus A shows itself as “a shadow”, or more precisely, as an absorption feature (the wavelength is 1-2 micrometers). The Spitzer images represent somewhat longer wavelengths, and show the radiation emitted by the dust itself. As a concrete example, the most famous Spitzer image of Centaurus A … shows a parallelogram-like structure, but the image describes radiation mainly from dust, not from stars,” he said.

There is a large, S- or bar-shaped dust lane straight through the center of Centaurus A that obscures observations in the visible light spectrum. As shown in the image below, the ring structure of star formation is obscured by dust, but visible in the near-infrared.

Centaurus A is believe to house a supermassive black hole that has the mass of 200 million Suns at its core, evidenced by the radio emissions streaming out from the galaxy. Previous images of the galaxy from the Spitzer Space Telescope, the ESA’s Infrared Space Observatory and the Hubble Space Telescope revealed some aspects of the structure of the galaxy. The infrared eyes of Spitzer peered partway through the dust to show a warped parallelogram, the cause of which is the gravitational disturbance caused by the merger of Centaurus A with a smaller spiral galaxy.

The presence of rings such as the one seen in Centaurus A is probably not common among other elliptical galaxies, but other such galaxies are known to exist. It’s possible that they are present during only certain periods of an elliptical galaxy’s formation after it merges with another galaxy.

Dr. Kainulainen commented on this possiblity: “One should consider that seeing so bright ring structure is probably quite time-critical. The rings are believed to be induced by “a violent event” of merging galaxies, and they may evolve rather quickly to something that no longer looks like a clear, bright ring. Therefore, they might actually be quite common for merging galaxies, but they “last” only such a short time that we don’t see them in so many galaxies.”

The analysis technique used by the team could be applied to other galaxies to resolve formation structures previously hidden by dust, and provide more information about how violent events alter the formation of elliptical galaxies.

“Potentially, the technique can be applied to any relatively nearby galaxy showing prominent dust features. Such targets could be M31, M83, M51, Fornax A, or any similarly large, bright, dust containing galaxy. Due to geometrical reasons, Centaurus A was a very suitable target for applying the method. It will be more challenging in the case of, for example, normal Spiral galaxies. However, we have already experimented with such galaxies and feel positive about the possibilities they give,” said Dr. Kainulainen.

The striking image of Centaurus A’s ring of star formation was a somewhat surprising result of the imaging that the astronomers took of the galaxy, though there were hints from images taken by other telescopes that stellar formation was present in the obscured, dusty core.

Dr. Kainulainen said, “It was very surprising that the structure contained so much stars and star-forming activity, and that we could reveal it in such great detail. However, it was expected that a structure of this kind exists there, and contains at least some star formation. This was evident, for example, from the earlier Spitzer images. But when I first saw our result, “The Naked Picture of Centaurus A”, on my computer screen, it really was a big WOW-feeling!”

Further observations of Centaurus A are definitely in order to further explore the structure of the stellar ring, and the gravitational dynamics that allowed for its formation.

“Our plans include observations with the Very Large Telescope (European Southern Observatory) and the Hubble Space Telescope. In that work, the information we got about the dust lane in our published Letter will play a significant role. The planned observations aim particularly at determining how long, and in what magnitude, the structure has been forming stars in the past. Such information will help to understand galaxy-merging process, which is not an uncommon event in the Universe.

Dr. Kainulainen and his team published their results in a letter to Astronomy & Astrophysics, published online July 2nd, 2009. The full text of the letter is available here.

Source: ESO, Astronomy and Astrophysics, email interview with Jouni Kainulainen