Friday, February 05, 2016

One from many

Credit:ESA/Hubble & NASA
Acknowledgement: Judy Schmidt (
Geckzilla)


This image, taken by the NASA/ESA Hubble Space Telescope, shows a peculiar galaxy known as NGC 1487, lying about 30 million light-years away in the southern constellation of Eridanus.

Rather than viewing a celestial object, it is actually better to think of this as an event. Here, we are witnessing two or more galaxies in the act of merging together to form a single new galaxy. Each progenitor has lost almost all traces of its original appearance, as stars and gas have been thrown hither and thither by gravity in an elaborate cosmic whirl.

Unless one is very much bigger than the other, galaxies are always disrupted by the violence of the merging process. As a result, it is very difficult to determine precisely what the original galaxies looked like and, indeed, how many of them there were. In this case, it is possible that we are seeing the merger of several dwarf galaxies that were previously clumped together in a small group.

Although older yellow and red stars can be seen in the outer regions of the new galaxy, its appearance is dominated by large areas of bright blue stars, illuminating the patches of gas that gave them life. This burst of star formation may well have been triggered by the merger.



Thursday, February 04, 2016

Moon was produced by a head-on collision between Earth and a forming planet

The extremely similar chemical composition of rocks on the Earth and moon helped scientists determine that a head-on collision, not a glancing blow, took place between Earth and Theia. Copyright William K. Hartmann

Paul Warren, Edward Young (holding a sample of a rock from the moon) and Issaku Kohl
Credit: Christelle Snow/UCLA


UCLA-led research reconstructs massive crash, which took place 4.5 billion years ago


The moon was formed by a violent, head-on collision between the early Earth and a “planetary embryo” called Theia approximately 100 million years after the Earth formed, UCLA geochemists and colleagues report.

Scientists had already known about this high-speed crash, which occurred almost 4.5 billion years ago, but many thought the Earth collided with Theia (pronounced THAY-eh) at an angle of 45 degrees or more — a powerful side-swipe (simulated in this 2012 YouTube video). New evidence reported Jan. 29 in the journal Science substantially strengthens the case for a head-on assault.

The researchers analyzed seven rocks brought to the Earth from the moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth’s mantle — five from Hawaii and one from Arizona.

The key to reconstructing the giant impact was a chemical signature revealed in the rocks’ oxygen atoms. (Oxygen makes up 90 percent of rocks’ volume and 50 percent of their weight.) More than 99.9 percent of Earth’s oxygen is O-16, so called because each atom contains eight protons and eight neutrons. But there also are small quantities of heavier oxygen isotopes: O-17, which have one extra neutron, and O-18, which have two extra neutrons. Earth, Mars and other planetary bodies in our solar system each has a unique ratio of O-17 to O-16 — each one a distinctive “fingerprint.”

In 2014, a team of German scientists reported in Science that the moon also has its own unique ratio of oxygen isotopes, different from Earth’s. The new research finds that is not the case.

“We don’t see any difference between the Earth’s and the moon’s oxygen isotopes; they’re indistinguishable,” said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.

Young’s research team used state-of-the-art technology and techniques to make extraordinarily precise and careful measurements, and verified them with UCLA’s new mass spectrometer.

The fact that oxygen in rocks on the Earth and our moon share chemical signatures was very telling, Young said. Had Earth and Theia collided in a glancing side blow, the vast majority of the moon would have been made mainly of Theia, and the Earth and moon should have different oxygen isotopes. A head-on collision, however, likely would have resulted in similar chemical composition of both Earth and the moon.

“Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” Young said. “This explains why we don’t see a different signature of Theia in the moon versus the Earth.”

Theia, which did not survive the collision (except that it now makes up large parts of Earth and the moon) was growing and probably would have become a planet if the crash had not occurred, Young said. Young and some other scientists believe the planet was approximately the same size as the Earth; others believe it was smaller, perhaps more similar in size to Mars.

Another interesting question is whether the collision with Theia removed any water that the early Earth may have contained. After the collision — perhaps tens of millions of year later — small asteroids likely hit the Earth, including ones that may have been rich in water, Young said. Collisions of growing bodies occurred very frequently back then, he said, although Mars avoided large collisions.

A head-on collision was initially proposed in 2012 by Matija Ćuk, now a research scientist with the SETI Institute, and Sarah Stewart, now a professor at UC Davis; and, separately during the same year by Robin Canup of the Southwest Research Institute.

Co-authors of the Science paper are Issaku Kohl, a researcher in Young’s laboratory; Paul Warren, a researcher in the UCLA department of Earth, planetary, and space sciences; David Rubie, a research professor at Germany’s Bayerisches Geoinstitut, University of Bayreuth; and Seth Jacobson and Alessandro Morbidelli, planetary scientists at France’s Laboratoire Lagrange, Université de Nice.

The research was funded by NASA, the Deep Carbon Observatory and a European Research Council advanced grant (ACCRETE).


Media Contact

Stuart Wolpert
310-206-0511
swolpert@support.ucla.edu


Wednesday, February 03, 2016

The Deep-Frozen Flying Saucer

PR Image eso1604a 
The Flying Saucer protoplanetary disc around 2MASS J16281370-2431391
The Flying Saucer protoplanetary disc around 2MASS J16281370-2431391
The Rho Ophiuchi star formation region in the constellation of Ophiuchus

The Rho Ophiuchi star formation region in the constellation of Ophiuchus

Zooming in on the Flying Saucer protoplanetary disc


ALMA finds unexpectedly cold grains in planet-forming disc

Astronomers have used the ALMA and IRAM telescopes to make the first direct measurement of the temperature of the large dust grains in the outer parts of a planet-forming disc around a young star. By applying a novel technique to observations of an object nicknamed the Flying Saucer they find that the grains are much colder than expected: −266 degrees Celsius. This surprising result suggests that models of these discs may need to be revised.

The international team, led by Stephane Guilloteau at the Laboratoire d'Astrophysique de Bordeaux, France, measured the temperature of large dust grains around the young star 2MASS J16281370-2431391 in the spectacular Rho Ophiuchi star formation region, about 400 light-years from Earth.

This star is surrounded by a disc of gas and dust — such discs are called protoplanetary discs as they are the early stages in the creation of planetary systems. This particular disc is seen nearly edge-on, and its appearance in visible light pictures has led to its being nicknamed the Flying Saucer.

The astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the glow coming from carbon monoxide molecules in the 2MASS J16281370-2431391 disc. They were able to create very sharp images and found something strange — in some cases they saw a negative signal! Normally a negative signal is physically impossible, but in this case there is an explanation, which leads to a surprising conclusion.

Lead author Stephane Guilloteau takes up the story: “This disc is not observed against a black and empty night sky. Instead it’s seen in silhouette in front of the glow of the Rho Ophiuchi Nebula. This diffuse glow is too extended to be detected by ALMA, but the disc absorbs it. The resulting negative signal means that parts of the disc are colder than the background. The Earth is quite literally in the shadow of the Flying Saucer!

The team combined the ALMA measurements of the disc with observations of the background glow made with the IRAM 30-metre telescope in Spain [1]. They derived a disc dust grain temperature of only −266 degrees Celsius (only 7 degrees above absolute zero, or 7 Kelvin) at a distance of about 15 billion kilometres from the central star [2]. This is the first direct measurement of the temperature of large grains (with sizes of about one millimetre) in such objects.

This temperature is much lower than the −258 to −253 degrees Celsius (15 to 20 Kelvin) that most current models predict. To resolve the discrepancy, the large dust grains must have different properties than those currently assumed, to allow them to cool down to such low temperatures.

To work out the impact of this discovery on disc structure, we have to find what plausible dust properties can result in such low temperatures. We have a few ideas — for example the temperature may depend on grain size, with the bigger grains cooler than the smaller ones. But it is too early to be sure,” adds co-author Emmanuel di Folco (Laboratoire d'Astrophysique de Bordeaux).

If these low dust temperatures are found to be a normal feature of protoplanetary discs this may have many consequences for understanding how they form and evolve.

For example, different dust properties will affect what happens when these particles collide, and thus their role in providing the seeds for planet formation. Whether the required change in dust properties is significant or not in this respect cannot yet be assessed.

Low dust temperatures can also have a major impact for the smaller dusty discs that are known to exist. If these discs are composed of mostly larger, but cooler, grains than is currently supposed, this would mean that these compact discs can be arbitrarily massive, so could still form giant planets comparatively close to the central star.

Further observations are needed, but it seems that the cooler dust found by ALMA may have significant consequences for the understanding of protoplanetary discs.



Notes:

[1] The IRAM measurements were needed as ALMA itself was not sensitive to the extended signal from the background.

 [2] This corresponds to one hundred times the distance from the Earth to the Sun. This region is now occupied by the Kuiper Belt within the Solar System.



More information

This research was presented in a paper entitled “The shadow of the Flying Saucer: A very low temperature for large dust grains”, by S. Guilloteau et al., published in Astronomy & Astrophysics Letters.

The team is composed of S. Guilloteau (University of Bordeaux/CNRS, Floirac, France), V. Piétu (IRAM, Saint Martin d’Hères, France), E. Chapillon (University of Bordeaux/CNRS; IRAM), E. Di Folco (University of Bordeaux/CNRS), A. Dutrey (University of Bordeaux/CNRS), T.Henning (Max Planck Institute für Astronomie, Heidelberg, Germany [MPIA]), D.Semenov (MPIA), T.Birnstiel (MPIA) and N. Grosso (Observatoire Astronomique de Strasbourg, Strasbourg, France).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

The Institut de Radio Astronomie Millimétrique (IRAM) is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.




Links



Contacts

Stephane Guilloteau
Laboratoire d'Astrophysique de Bordeaux
Floirac, France
Email: stephane.guilloteau@u-bordeaux.fr

Emmanuel di Folco
Laboratoire d'Astrophysique de Bordeaux
Floirac, France
Email: emmanuel.di-folco@u-bordeaux.fr

Vincent Pietu
IRAM
Grenoble, France
Email: pietu@iram.fr

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org


Source: ESO

Supermassive Black Hole - That Wasn't

Figure 1. GMOS-South image of the center of the Abell 85 galaxy cluster. The brightest galaxy in the middle was thought to hide a supermassive black hole in its core based on prior lower-resolution data. 

Figure 2. Surface brightness profile of the brightest cluster galaxy in Abell 85. The top panel presents the light emanating from that galaxy in the inner 6 kiloparsecs. The new Gemini data show a light excess, visible as a bump in the very center of the profile. In contrast, earlier observations (black) had suggested a light deficit at the core, but this is an artifact of their lower resolution.  


Research shows that supermassive black holes like to be the only residents on the block, as stars too close to them end up being thrown vast distances from the galaxy's center. As black holes eject stars around them, the neighborhood becomes darker. Astronomers have been hunting for these gloomy neighborhoods in galaxy cores for decades. The signature of supermassive black holes are known as light deficits, due to the lack of stars surrounding them. 

Gemini Science Fellow, Juan Madrid and Carlos Donzelli from the Cordoba observatory in Argentina were granted observations through the Director's Discretionary Time, and used new Gemini data to study the brightest galaxy of the galaxy cluster Abell 85 to verify earlier observations hinting that one of the most supermassive black holes ever discovered resided at the galaxy's core.

Gemini sets the record straight - in seven minutes

The Gemini Multi Object Spectrograph (GMOS) at Gemini South needed only seven minutes of observations to reveal that the brightest galaxy of Abell 85 does not have a light deficit. On the contrary, the high resolution of the Gemini data show that the core of this galaxy has a light excess incompatible with the theory that it hosts an especially massive black hole.

Paper Abstract:

New high-resolution r band imaging of the brightest cluster galaxy (BCG) in Abell 85 (Holm 15A) was obtained using the Gemini Multi Object Spectrograph. These data were taken with the aim of deriving an accurate surface brightness profile of the BCG of Abell 85, in particular its central region. The new Gemini data show clear evidence of a previously unreported nuclear emission that is evident as a distinct light excess in the central kiloparsec of the surface brightness profile. We find that the light profile is never flat nor does it present a downward trend towards the center of the galaxy. That is, the new Gemini data show a different physical reality from the featureless, "evacuated core" recently claimed for the Abell 85 BCG. After trying different models, we find that the surface brightness profile of the BCG of Abell 85 is best fit by a double Sérsic model.



Tuesday, February 02, 2016

Pictor A: Blast from Black Hole in a Galaxy Far, Far Away

 Pictor A
Credit: X-ray: NASA/CXC/Univ of Hertfordshire/M.Hardcastle et al., Radio: CSIRO/ATNF/ATCA

animation


The Star Wars franchise has featured the fictitious "Death Star," which can shoot powerful beams of radiation across space. The Universe, however, produces phenomena that often surpass what science fiction can conjure.

The Pictor A galaxy is one such impressive object. This galaxy, located nearly 500 million light years from Earth, contains a supermassive black hole at its center. A huge amount of gravitational energy is released as material swirls towards the event horizon, the point of no return for infalling material. This energy produces an enormous beam, or jet, of particles traveling at nearly the speed of light into intergalactic space.

To obtain images of this jet, scientists used NASA's Chandra X-ray Observatory at various times over 15 years. Chandra's X-ray data (blue) have been combined with radio data from the Australia Telescope Compact Array (red) in this new composite image.

By studying the details of the structure seen in both X-rays and radio waves, scientists seek to gain a deeper understanding of these huge collimated blasts.

The jet [to the right] in Pictor A is the one that is closest to us. It displays continuous X-ray emission over a distance of 300,000 light years. By comparison, the entire Milky Way is about 100,000 light years in diameter. Because of its relative proximity and Chandra's ability to make detailed X-ray images, scientists can look at detailed features in the jet and test ideas of how the X-ray emission is produced.

In addition to the prominent jet seen pointing to the right in the image, researchers report evidence for another jet pointing in the opposite direction, known as a "counterjet". While tentative evidence for this counterjet had been previously reported, these new Chandra data confirm its existence. The relative faintness of the counterjet compared to the jet is likely due to the motion of the counterjet away from the line of sight to the Earth.

The labeled image shows the location of the supermassive black hole, the jet and the counterjet. Also labeled is a "radio lobe" where the jet is pushing into surrounding gas and a "hotspot" caused by shock waves - akin to sonic booms from a supersonic aircraft - near the tip of the jet.

The detailed properties of the jet and counterjet observed with Chandra show that their X-ray emission likely comes from electrons spiraling around magnetic field lines, a process called synchrotron emission. In this case, the electrons must be continuously re-accelerated as they move out along the jet. How this occurs is not well understood

The researchers ruled out a different mechanism for producing the jet's X-ray emission. In that scenario, electrons flying away from the black hole in the jet at near the speed of light move through the sea of cosmic background radiation (CMB) left over from the hot early phase of the Universe after the Big Bang. When a fast-moving electron collides with one of these CMB photons, it can boost the photon's energy up into the X-ray band.

The X-ray brightness of the jet depends on the power in the beam of electrons and the intensity of the background radiation. The relative brightness of the X-rays coming from the jet and counterjet in Pictor A do not match what is expected in this process involving the CMB, and effectively eliminate it as the source of the X-ray production in the jet.

A paper describing these results will be published in the Monthly Notices of the Royal Astronomical Society and is available online. The authors are Martin Hardcastle from the University of Hertfordshire in the UK, Emil Lenc from the University of Sydney in Australia, Mark Birkinshaw from the University of Bristol in the UK, Judith Croston from the University of Southampton in the UK, Joanna Goodger from the University of Hertfordshire, Herman Marshall from the Massachusetts Institute of Technology in Cambridge, MA, Eric Perlman from the Florida Institute of Technology, Aneta Siemiginowska from the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, Lukasz Stawarz from Jagiellonian University in Poland and Diana Worrall from the University of Bristol.

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


Fast Facts for Pictor A:

Scale: Image is 10 arcmin across (about 1.4 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 05h 19m 49.70s | Dec -45° 46' 45"
Constellation: Pictor
Observation Date: 14 pointings between Jan 2000 and Jan 2015
Observation Time: 128 hours 53 min (5 days 8 hours 53 min)
Obs. ID: 346, 3090, 4369, 12039, 12040, 11586, 14357, 14221, 15580, 15593, 14222, 14223, 16478, 17574
Instrument: ACIS
References: Hardcastle, M. et al., 2016, MNRAS, 455, 3526; arXiv:1510.08392
Color Code: X-ray (Blue), Radio (Red)
Distance Estimate: About 480 million light years (z=0.035)



The Unearthly Beauty of the Red Rectangle

The Unearthly Beauty of the Red Rectangle
Copyright: ESA/Hubble and NASA
Hi-res JPG - TIF

Straight lines do not often crop up in space. Whenever they do, they seem somehow incongruous and draw our attention. The Red Rectangle is one such mystery object.

It first caught astronomers’ attention in 1973. The star HD 44179 had been known since 1915 to be double, but it was only when a rocket flight carrying an infrared detector was turned its way that the red rectangle revealed itself.

This image was taken later, in 2007, by the Hubble Space Telescope’s Advanced Camera for Surveys. It focuses on wavelengths of red light, in particular highlighting the emission from hydrogen gas.

This particular emission has been displayed in red. A second, broader range of orange–red light has also been recorded, and, to increase the contrast, this light has been colour coded blue on the image.

The Red Rectangle is some 2300 light-years away in the constellation of Monoceros. It arises because one of the stars in HD 44179 is in the last stages of its life. It has puffed up as the nuclear reactions at its core have faltered, and this has resulted in it shedding its outer layers into space.

Such a cloud of gas is known erroneously as a planetary nebula because Hanoverian astronomer William Herschel thought they look a bit like the pale disc of Uranus, the planet he had discovered.

The X-shape revealed in this image suggests that something is preventing the uniform expansion of the star’s atmosphere. Instead, a thick disc of dust probably surrounds the star, funnelling the outflow into two wide cones. The edges of these show up as the diagonal lines. Thankfully, while that explains the mystery of the object, it does not detract from its unearthly beauty.

This image was first published in June 2010.

Source: ESA/Images

Monday, February 01, 2016

Where are all of the nebulae ionized by supersoft X-ray sources?

Artist's depiction of an accreting white dwarf
© David A. Hardy/AstroArt.org


The ultimate fate of low-mass stars, like our own Sun, is to exhaust the nuclear furnace in their cores, expel their extended atmospheres, and leave behind a hot remnant called a white dwarf. Left to their own devices, these objects will simply cool slowly over billions of years. However, if a white dwarf comes to accrete material from some stellar companion, it can become an incredibly luminous source of extreme UV and soft X-ray emission, a “supersoft X-ray source” or SSS. Such radiation is readily absorbed by any surrounding interstellar gas, producing emission line nebulae. Therefore, we would expect such nebulae to be found accompanying all supersoft X-ray sources. However, of all SSSs found in the past three decades, only one has been observed to have such a nebula. Clearly, something is amiss in our understanding of these incredible objects. Now, scientists at MPA and the Monash Centre for Astrophysics have pieced together the puzzle.

Under the right conditions, a white dwarf accreting hydrogen-rich matter from a binary companion can process all of this material through nuclear burning at its surface, with luminosities and temperatures of thousands of times that of our Sun (1038 erg/s and 105K-106K, respectively). First discovered more than 30 years ago by NASA's Einstein observatory, these close binary supersoft X-ray sources soon became favoured candidates for the progenitors of type Ia supernovae: as white dwarfs accrete material, they may grow to reach the Chandrasekhar mass limit and explode. However, testing this hypothesis by trying to find the true number of such objects has been complicated by the great ease with which the emitted extreme UV and soft X-ray photons are completely absorbed by even a modest amount of intervening interstellar matter.

Therefore, an alternative approach is to use this absorption and search for nebular emission lines in interstellar matter that is ionized by these hot, luminous sources [1,2]. However, narrow-band observations of the vicinity of supersoft X-ray sources in the Magellanic Clouds revealed only one such nebula [3]. This led to a vexing question: is there something very wrong in our understanding of the nature of these sources? 

Or is there something special about the interstellar environment of CAL 83, where the nebula was found, ­ and not every other SSS? This dilemma put emission line studies of supersoft X-ray sources largely on hold for the next two decades.

In their recent work [4], Tyrone Woods (formerly at MPA, now a research fellow at the Monash Centre for Astrophysics) and Marat Gilfanov (MPA) noted that the gaseous nebula surrounding CAL 83 is at least ten-fold overdense relative to the gas densities found in most of the volume of typical star-forming galaxies. The high surface brightness nebula of CAL 83 thus appears to be the result of a chance encounter of the accreting white dwarf with a region of initially cold, dense interstellar matter. Additional analysis of the size and distribution of cold dense clouds in galaxies (with the aid of mathematics borrowed from the study of concrete porosity) provided further support for this interpretation. 

ISM density (vertical axis) required to produce a detectable nebula ionized by a accreting white dwarf (2x10^5 K, with bolometric luminosity L, horizontal axis). The three lines denote a signal-to-noise ratio of 50, i.e. clear detection, for 150, 1500, and 9000 seconds total integration times using the Magellan Baade telescope. For reference, the inferred density and time-averaged luminosity of CAL 83 is also shown. © MPA

Most supersoft X-ray sources are likely to lie in much lower density media, with correspondingly lower surface brightness nebulae, which extend to larger radii (up to more than 100 parsecs, compared with 10 parsecs for CAL 83). Even though such nebulae are below the detection threshold of past observations, they are detectable given modest integration times with large modern telescopes such as Magellan or the VLT (see fig. 2).

This not only re-opens a channel for the study of close binary supersoft X-ray sources; given that the decay time for any SSS nebula will be on the order of ten thousand to a hundred thousand years, one may also search for “fossil” nebulae surrounding the sites of SSSs, which have long since stopped accreting. In particular, this includes those that may have exploded as type Ia supernovae in the recent past and in our cosmic neighbourhood. This means that one should be able to resolve the surrounding nebula and inner supernova remnant separately. A deep narrow-band search using the Magellan Baade telescope is already underway, and we may soon measure (or tightly constrain) the temperatures and luminosities of the progenitors of nearby type Ia supernova remnants.


Authors :  Woods, T. E., & Gilfanov, M.


References:

1. Rappaport, S., Chiang, E., Kallman, T., & Malina, R.
Ionization nebulae surrounding supersoft X-ray sources.
1994, APJ, 431, 237.  Source

2. Woods, T. E., & Gilfanov, M.
He II recombination lines as a test of the nature of SN Ia progenitors in elliptical galaxies.
2013, MNRAS, 432, 1640.  Source

3. Remillard, R. A., Rappaport, S., & Macri, 
L. M. Ionization nebulae surrounding CAL 83 and other supersoft X-ray sources. 1995, ApJ, 439, 64.  Source

4. Woods, T. E. & Gilfanov, M.
Where are all of the nebulae ionized by supersoft X-ray sources?
2016, MNRAS, 455, 1770.  Source



Lonely planet finds mum a trillion kilometres away

Artist's impression of the planet with its star in the background
Credit: Neil James Cook/University of Hertfordshire
 
 2MASS J2126−8140 and TYC 9486-927-1,
False colour infrared image. Arrows shows motion over next 1.000 years
Credit: Simon Murphy


Astronomers studying a lonely planet drifting through space have found its mum; a star a trillion kilometres away.

The planet, known as 2MASS J2126−8140, has an orbit around its host star that takes nearly a million Earth years and is more than 140 times wider than Pluto's. This makes it easily the largest solar system ever found.

"We were very surprised to find such a low-mass object so far from its parent star," said Dr Simon Murphy of ANU Research School of Astronomy and Astrophysics.

"There is no way it formed in the same way as our solar system did, from a large disc of dust and gas."

Only a handful of extremely wide pairs of this kind have been found in recent years. The distance between the new pair is 6,900 Astronomical Units (AU) - 1,000,000,000,000 kilometres or 0.1 light years - nearly three times the previous widest pair, which is 2,500AU (370,000,000,000 km).

2MASS J2126−8140's parent is a red dwarf star called TYC 9486-927-1. At that distance, it would appear as only a moderately bright star in the sky, and light would take about a month to reach the planet.

Dr Murphy is part of an international team of scientists that studied 2MASS J2126−8140, a gas giant planet around 12 to 15 times the mass of Jupiter, as part of a survey of several thousand young stars and brown dwarfs close to our solar system.

Once they realised 2MASS J2126−8140 and TYC 9486-927-1 were a similar distance from the Earth - about 100 light years - they compared the motion of the two through space and realised they were moving together.

"We can speculate they formed 10 million to 45 million years ago from a filament of gas that pushed them together in the same direction," Dr Murphy said.

"They must not have lived their lives in a very dense environment. They are so tenuously bound together that any nearby star would have disrupted their orbit completely."

The research, which will be published in the Monthly Notices of The Royal Astronomical Society, was led by Dr Niall Deacon from University of Hertfordshire and included Dr Joshua Schlieder from the NASA Ames Research Center.



Friday, January 29, 2016

Monstrous Cloud Boomerangs Back to Our Galaxy

Trajectory of Smith Cloud
This diagram shows the 100-million-year-long trajectory of the Smith Cloud as it arcs out of the plane of our Milky Way galaxy and then returns like a boomerang. Hubble Space Telescope measurements show that the cloud, because of its chemical composition, came out of a region near the edge of the galaxy's disk of stars 70 million years ago. The cloud is now stretched into the shape of a comet by gravity and gas pressure. Following a ballistic path, the cloud will fall back into the disk and trigger new star formation 30 million years from now. Illustration Credit: NASA, ESA, and A. Feild (STScI) - Science Credit: NASA, ESA, and A. Fox (STScI)
 
Size of Smith Cloud on the Sky
This composite image shows the size and location of the Smith Cloud on the sky. The cloud appears in false-color, radio wavelengths as observed by the Robert C. Byrd Green Bank Telescope in West Virginia. The visible-light image of the background star field shows the cloud's location in the direction of the summer constellation Aquila. The cloud is 15 degrees across in angular size — the width of an outstretched hand at arm's length. The apparent size of the full moon is added for comparison.

 Hubble Characterizes the High-Velocity Smith Cloud
The infalling Smith Cloud does not emit light at wavelengths that the Hubble Space Telescope is sensitive to. However, Hubble's Cosmic Origins Spectrograph can measure how the light from distant background objects is affected as it passes through the cloud. These measurements yield clues to the chemical composition of the cloud. By using these intergalactic forensics, Hubble astronomers trace the cloud's origin to the disk of our Milky Way. Combined ultraviolet and radio observations correlate to the cloud's infall velocities, providing solid evidence that the spectral features link to the cloud's dynamics.  Illustration Credit: NASA, ESA, and A. Feild (STScI) - Science Credit: NASA, ESA, and A. Fox (STScI)



Hubble Space Telescope astronomers are finding that the old adage "what goes up must come down" even applies to an immense cloud of hydrogen gas outside our Milky Way galaxy. The invisible cloud is plummeting toward our galaxy at nearly 700,000 miles per hour.

Though hundreds of enormous, high-velocity gas clouds whiz around the outskirts of our galaxy, this so-called "Smith Cloud" is unique because its trajectory is well known. New Hubble observations suggest it was launched from the outer regions of the galactic disk, around 70 million years ago. The cloud was discovered in the early 1960s by doctoral astronomy student Gail Smith, who detected the radio waves emitted by its hydrogen.

The cloud is on a return collision course and is expected to plow into the Milky Way's disk in about 30 million years. When it does, astronomers believe it will ignite a spectacular burst of star formation, perhaps providing enough gas to make 2 million suns.

"The cloud is an example of how the galaxy is changing with time," explained team leader Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland. "It's telling us that the Milky Way is a bubbling, very active place where gas can be thrown out of one part of the disk and then return back down into another."

"Our galaxy is recycling its gas through clouds, the Smith Cloud being one example, and will form stars in different places than before. Hubble's measurements of the Smith Cloud are helping us to visualize how active the disks of galaxies are," Fox said.

Astronomers have measured this comet-shaped region of gas to be 11,000 light-years long and 2,500 light-years across. If the cloud could be seen in visible light, it would span the sky with an apparent diameter 30 times greater than the size of the full moon.

Astronomers long thought that the Smith Cloud might be a failed, starless galaxy, or gas falling into the Milky Way from intergalactic space. If either of these scenarios proved true, the cloud would contain mainly hydrogen and helium, not the heavier elements made by stars. But if it came from within the galaxy, it would contain more of the elements found within our sun.

The team used Hubble to measure the Smith Cloud's chemical composition for the first time, to determine where it came from. They observed the ultraviolet light from the bright cores of three active galaxies that reside billions of light-years beyond the cloud. Using Hubble's Cosmic Origins Spectrograph, they measured how this light filters through the cloud.

In particular, they looked for sulfur in the cloud which can absorb ultraviolet light. "By measuring sulfur, you can learn how enriched in sulfur atoms the cloud is compared to the sun," Fox explained. Sulfur is a good gauge of how many heavier elements reside in the cloud.

The astronomers found that the Smith Cloud is as rich in sulfur as the Milky Way's outer disk, a region about 40,000 light-years from the galaxy's center (about 15,000 light-years farther out than our sun and solar system). This means that the Smith Cloud was enriched by material from stars. This would not happen if it were pristine hydrogen from outside the galaxy, or if it were the remnant of a failed galaxy devoid of stars. Instead, the cloud appears to have been ejected from within the Milky Way and is now boomeranging back.

Though this settles the mystery of the Smith Cloud's origin, it raises new questions: How did the cloud get to where it is now? What calamitous event could have catapulted it from the Milky Way's disk, and how did it remain intact? Could it be a region of dark matter — an invisible form of matter — that passed through the disk and captured Milky Way gas? The answers may be found in future research.

The team's research appears in the January 1, 2016, issue of The Astrophysical Journal Letters.


Contact: 

Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu

Andrew Fox
Space Telescope Science Institute, Baltimore, Maryland
410-338-5083
afox@stsci.edu

Source: HubbleSite

A misbehaving spiral

Credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt


Despite its unassuming appearance, the edge-on spiral galaxy captured in the left half of this NASA/ESA Hubble Space Telescope image is actually quite remarkable.

Located about one billion light-years away in the constellation of Eridanus, this striking galaxy — known as LO95 0313-192 — has a spiral shape similar to that of the Milky Way. It has a large central bulge, and arms speckled with brightly glowing gas mottled by thick lanes of dark dust. Its companion, sitting pretty in the right of the frame, is known rather unpoetically as [LOY2001] J031549.8-190623.

Jets, outbursts of superheated gas moving at close to the speed of light, have long been associated with the cores of giant elliptical galaxies, and galaxies in the process of merging. However, in an unexpected discovery, astronomers found LO95 0313-192 to have intense radio jets spewing out from its centre! The galaxy appears to have two more regions that are also strongly emitting in the radio part of the spectrum, making it even rarer still.

The discovery of these giant jets in 2003 — not visible in this image, but indicated in this earlier Hubble composite — has been followed by the unearthing of a further three spiral galaxies containing radio-emitting jets in recent years. This growing class of unusual spirals continues to raise significant questions about how jets are produced within galaxies, and how they are thrown out into the cosmos.



Thursday, January 28, 2016

Searching for Orbiting Companion Stars

A Hubble image of the star Gliese 229 together with its brown dwarf companion, Gliese 229B. A new systematic radial velocity search for brown dwarf and stellar-mass companions to stars has discovered one new giant exoplanet and four new companion stars. NASA/Hubble


The search for exoplanets via the radial velocity technique has been underway for nearly 30 years. The method searches for wobbles in a star's motion caused by the presence of orbiting bodies. It has been has been very successful, detecting hundreds of exoplanets, but has been overtaken (at least in numbers of detections) by the transit method, which looks for dips in the star's light. The velocity technique also naturally spots orbiting bodies that are larger than planets, which can be either stellar-mass companions or smaller companions that are not quite large enough to become stars, called brown-dwarfs. These larger companions have been largely ignored by surveys dedicated to finding exoplanets, but they are valuable discoveries for astronomers trying to study the smallest classes of stars which are very dim and otherwise difficult to detect.

The indications so far are that there are fewer brown dwarf stars than expected in the mass range from about 13 to 80 Jupiter-masses, a phenomenon known as the "brown dwarf desert" that is unexplained. There is another important puzzle: About half of all nearby stars are binary systems yet there are very few known exoplanets around them - only about five percent of all known exoplanets. The dynamics of forming a planetary system around (or within) a multiple-star system are complex and important but poorly understood.

CfA astronomer John Johnson and six colleagues decided to study brown dwarf stars directly with a dedicated, five-year survey that emphasized large companions (stars or brown dwarfs) to mid-sized stars. 

The scientists selected forty-eight candidate stars for detailed observations from an initial sample of 167 likely candidates based on preliminary observations. They discovered one new giant exoplanet in this set and four stellar-mass companions, one of which may in fact be a brown dwarf. All the objects orbit their stars at distances less than a few astronomical units (one AU is the average distance of the Earth from the Sun). The new results include the orbital parameters of the objects, and the paper considers the possibility of imaging directly these multiple systems with a new generation of optical instruments. The work also marks one of the first efforts to address the nature of the "brown-dwarf desert" by searching for them systematically in order to improve the statistics.

Reference (s):

"The Pan-Pacific Planet Search III: five Companions orbiting giant stars," R. A. Wittenmyer, R. P. Butler, L. Wang, C. Bergmann, G. S. Salter, C. G. Tinney and J. A. Johnson, MNRAS 445, 1398, 2016.



Wednesday, January 27, 2016

The Milky Way’s Clean and Tidy Galactic Neighbour

The dwarf galaxy IC 1613

PR Image eso1603b
The dwarf galaxy IC 1613 in the constellation of Cetus

The sky around the dwarf galaxy IC 1613


Videos

Zooming in on the dwarf galaxy IC 1613
Zooming in on the dwarf galaxy IC 1613

A close look at the dwarf galaxy IC 1613
A close look at the dwarf galaxy IC 1613

IC1613 Fulldome Flythrough
IC1613 Fulldome Flythrough


Many galaxies are chock-full of dust, while others have occasional dark streaks of opaque cosmic soot swirling in amongst their gas and stars. However, the subject of this new image, snapped with the OmegaCAM camera on ESO’s VLT Survey Telescope in Chile, is unusual — the small galaxy, named IC 1613, is a veritable clean freak! IC 1613 contains very little cosmic dust, allowing astronomers to explore its contents with great clarity. This is not just a matter of appearances; the galaxy’s cleanliness is vital to our understanding of the Universe around us.

IC 1613 is a dwarf galaxy in the constellation of Cetus (The Sea Monster). This VST image [1] shows the galaxy’s unconventional beauty, all scattered stars and bright pink gas, in great detail.

German astronomer Max Wolf discovered IC 1613’s faint glow in 1906. In 1928, his compatriot Walter Baade used the more powerful 2.5-metre telescope at the Mount Wilson Observatory in California to successfully make out its individual stars. From these observations, astronomers figured out that the galaxy must be quite close to the Milky Way, as it is only possible to resolve single pinprick-like stars in the very nearest galaxies to us.

Astronomers have since confirmed that IC 1613 is indeed a member of the Local Group, a collection of more than 50 galaxies that includes our home galaxy, the Milky Way. IC 1613 itself lies just over 2.3 million light-years away from us. It is relatively well-studied due to its proximity; astronomers have found it to be an irregular dwarf that lacks many of the features, such as a starry disc, found in some other diminutive galaxies.

However, what IC 1613 lacks in form, it makes up for in tidiness. We know IC 1613’s distance to a remarkably high precision, partly due to the unusually low levels of dust lying both within the galaxy and along the line of sight from the Milky Way — something that enables much clearer observations [2].

The second reason we know the distance to IC 1613 so precisely is that the galaxy hosts a number of notable stars of two types: Cepheid variables and RR Lyrae variables [3]. Both types of star rhythmically pulsate, growing characteristically bigger and brighter at fixed intervals (eso1311).

As we know from our daily lives on Earth, shining objects such as light bulbs or candle flames appear dimmer the further they are away from us. Astronomers can use this simple piece of logic to figure out exactly how far away things are in the Universe— so long as they know how bright they really are, referred to as their intrinsic brightness.

Cepheid and RR Lyrae variables have the special property that their period of brightening and dimming is linked directly to their intrinsic brightness. So, by measuring how quickly they fluctuate astronomers can work out their intrinsic brightness. They can then compare these values to their apparent measured brightness and work out how far away they must be to appear as dim as they do.

Stars of known intrinsic brightness can act like standard candles, as astronomers say, much like how a candle with a specific brightness would act as a good gauge of distance intervals based on the observed brightness of its flame’s flicker.

Using standard candles — such as the variable stars within IC 1613 and the less-common Type Ia supernova explosions, which can seen across far greater cosmic distances — astronomers have pieced together a cosmic distance ladder, reaching deeper and deeper into space.

Decades ago, IC 1613 helped astronomers work out how to utilise variable stars to chart the Universe’s grand expanse. Not bad for a little, shapeless galaxy.



Notes

[1] OmegaCAM is a 32-CCD, 256-million-pixel camera mounted on the 2.6-metre VLT Survey Telescope at Paranal Observatory in Chile. Click here to view more images taken by OmegaCAM.

[2] Cosmic dust is made of various heavier elements, such as carbon and iron, as well as larger, grainier molecules. Not only does dust block out light, making dust-shrouded objects harder to see, it also preferentially scatters bluer light. As a result, cosmic dust makes objects appear redder when seen through our telescopes than they are in reality. Astronomers can factor out this reddening when studying objects. Still, the less reddening, the more precise an observation is likely to be.

[3] Other than the two Magellanic Clouds, IC 1613 is the only irregular dwarf galaxy in the Local Group in which RR Lyrae type variable stars have been identified.



More Information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.



Link



Contacts

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org 


Source: ESO

The highest angular resolution image in Astronomy reveals the insides of a galactic nucleus


Credit: MPIfR/A. Lobanov


The space mission RadioAstron (Russian Space Agency) has observed, along with fifteen other radio telescopes spread across the globe, the environment of the black hole at the core of the active galaxy BL Lacertae

Since 1974, observations with very long baseline interferometry (VLBI) have combined the signals from a cosmic object received at different radio telescopes spread around the globe to synthetize an antenna with the equivalent size of the largest separation between them. This has provided unprecedented sharpness of the images, with over 1000 times better resolution than the Hubble Space Telescope can achieve in visible light. Now, an international collaboration has broken all records by combining fifteen radio telescopes on Earth and the radio dish of the RadioAstron mission (Russian Space Agency), in orbit around Earth. The work, lead by the Instituto de Astrofísica de Andalucía (IAA-CSIC), provides new insights into the nature of active galaxies, where an extremely massive black hole swallows surrounding matter while simultaneously shooting out a pair of jets of high-energy particles and magnetic fields at nearly light speed.

Observations of microwave light are essential for exploring these jets, since high-energy electrons moving in magnetic fields are very proficient at producing microwaves. But most active galaxies with bright jets are billions of light years away from Earth, so their jets are tiny on the sky. High resolution is essential for viewing the jets in action to reveal phenomena like shock waves and turbulence that control how much light is produced at any given time. “Combining for the first time ground-based radio telescopes with the space radio telescope of the RadioAstron mission, operating at its maximum resolution, has allowed our team to imitate an antenna with a size of eight times the Earth’s diameter, corresponding to about twenty microarcseconds”, said José L. Gómez, the team leader at the Instituto de Astrofísica de Andalucía (IAA-CSIC).

Seen from Earth, twenty microarcseconds corresponds to the size of a two euro coin on the Moon; this high resolution probes with unprecedented detail the central regions of BL Lacertae, an active galactic nucleus located nine hundred million light-years from Earth, powered by a supermassive black hole two hundred million times more massive than our Sun.

Artist concept showing how long base interferometry works. 
Credit:  MPIfR/A. Lobanov.


Extreme Sources

Active galactic nuclei (AGN) are the most energetic objects in the Universe, harboring a giant black hole at the center. Accretion of material toward the black hole leads to the formation of an accretion disk that tightly orbits the black hole, plus a pair of jets of particles shooting out of the nucleus in opposite directions at speeds nearly equal to that of light. “It is thought that jets originate from material drawn toward the black hole, but how the jets are collimated and accelerated is still largely unknown,” said Gómez. “We know, however, that the magnetic field should play an important role”.

Current models suggest that, due to the rotation of the black hole and accretion disk, the magnetic field lines are “twisted” into a spiral structure. Such a coiled field confines the jet to a narrow beam and accelerates its motion. This model is confirmed by the BL Lacertae observations, which reveal the existence of a large-scale spiral magnetic field in one of the jets.


Artist concept of an active galactic nuclei 
Credit: Wolfgang Steffen, UNAM.

The exceptional resolution obtained with RadioAstron also reveals an unusually intensity of light at the upstream end of BL Lacertae’s jet not observed before in other AGN. This is making astronomers wonder whether their established ideas on how the jets produce microwave light is correct.

“Our current understanding of how the emission is generated in AGN establishes a clear limit on the intensity of microwaves that their cores can produce over long time spans. The extreme intensity observed in BL Lacertae exceeds that limit, requiring either velocities in the jet even closer to the speed of light than thought before or a revision of our theoretical models”, concludes Jose L. Gómez (IAA-CSIC).


Reference:


J. L. Gómez et al. "Probing the innermost regions of AGN jets and their magnetic fields with Radioastron. I. Imaging BL Lacertae at 21 microarcsecond resolution". The Astrophysical Journal, 817, 96 (2016). DOI: 10.3847/0004-637X/817/2/96

http://iopscience.iop.org/article/10.3847/0004-637X/817/2/96


More información:

RadioAstron: http://www.asc.rssi.ru/radioastron/index.html

Contact:

Instituto de Astrofísica de Andalucía (IAA-CSIC)
Unidad de Divulgación y Comunicación
Silbia López de Lacalle - sll@iaa.es - 958230532
http://www.iaa.es
http://www-divulgacion.iaa.es



Tuesday, January 26, 2016

Galaxy cluster environment not dictated by its mass alone

The connection between internal structure of galaxy clusters and distribution of galaxy clusters
Credit: Sloan Digital Sky Survey, Kavli IPMU


An international team of researchers has found for the first time that the connection between a galaxy cluster and surrounding dark matter is not characterized solely by the mass of clusters, but also by their formation history.

Galaxy clusters are the biggest celestial objects in the sky consisting of thousands of galaxies. They form from nonuniformity in the matter distribution established by cosmic inflation in the beginning of the Universe. Their growth is a constant fight between the gathering of dark matter by gravity and the accelerated expansion of the universe due to dark energy. By studying galaxy clusters, researchers can learn more about these biggest and most mysterious building blocks of the Universe.

Led by Hironao Miyatake, (formerly JSPS fellow, currently at NASA’s Jet Propulsion Laboratory), Surhud More and Masahiro Takada of the Kavli Institute for the Physics and Mathematics (Kavli IPMU), the research team challenged the conventional idea that the connection between galaxy clusters and the surrounding dark matter environment is solely characterized by their mass. Based on the nature of the non-uniform matter distribution established by cosmic inflation, it was theoretically predicted that other factors should affect the connection. However, no one had succeeded in seeing it in the real Universe until now.

The team divided almost 9000 galaxy clusters from the Sloan Digital Sky Survey DR8 galaxy catalog into two samples based on the spatial distribution of galaxies inside each cluster. By using gravitational lensing they confirmed the two samples have similar masses, but they found that the distribution of clusters was different. Galaxy clusters in which member galaxies bunched up towards the center were less clumpy than clusters in which member galaxies were more spread out. The difference in distribution is a result of the different dark matter environment in which they form.

Researchers say their findings show that the connection between a galaxy cluster and surrounding dark matter is not characterized solely by the mass of clusters, but also by their formation history.

The results from this study would need to be taken into account in future large scale studies of the universe, and research looking into the nature of dark matter or dark energy, neutrinos, and the early universe.

The study will be published on January 25 in Physical Review Letters, and has been selected as an Editor’s Suggestion.



(from left) Authors Hironao Miyatake, Surhud More and Masahiro Takada
Credit: Kavli IPMU


Comment from Surhud More

“The signal we measure is puzzlingly large compared to naive theoretical estimates. The sheer number of tests for systematics that we had to perform to convince ourselves that the signal is real, was the most difficult part of this research.”

Comment from Masahiro Takada

“This is truly exciting finding! We can use the upcoming Subaru Hyper Suprime-Cam (HSC) data to further check and advance our understanding of the assembly history of galaxy clusters.”

Comment from Hironao Miyatake

“I am thrilled that we have finally found clear evidence of the connection between the internal structure of clusters and surrounding dark matter environment. We checked lots of things to make sure this result, and finally concluded this is real! I am also excited that our findings will give insights on many aspects of the universe, such as large scale structure, dark matter and dark energy, and inflation physics. It is just starting. We hope we can get more exciting results from the upcoming HSC data.”

Comment from David Spergel

“Cosmologist have long held a very simple theory: " the properties of a cluster is determined solely by its mass”. These results show that the situation is much more complex: the clusters environment also plays an important role. Astronomers have been trying to detect evidence for this more complex picture for many years: this is the first definitive detection.”

Paper Details

Journal: Physical Review Letters, vol 116 (2016)
Title: Evidence of halo assembly bias in massive clusters
Authors: Hironao Miyatake (1, 2, 3), Surhud More (2), Masahiro Takada (2), David N. Spergel (1, 2), Rachel Mandelbaum (4), Eli S. Rykoff (5, 6), Eduardo Rozo (7)

Author affiliations:

1 Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544, USA
2 Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo, Chiba, 277-8583, Japan
3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
4 McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
5 Kavli Institute for Particle Astrophysics & Cosmology, P. O. Box 2450, Stanford University, Stanford, CA 94305, USA
6 SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
7 Department of Physics, University of Arizona, 1118 E 4th St, Tucson, AZ 85721, USA 

DOI: 10.1103/PhysRevLett.116.041301

Paper Abstract (Physical Review Letters) - link to be added once available

Preprint (arXiv.org archive website)


Media contacts

Motoko Kakubayashi
Press Officer
Kavli Institute for the Physics and Mathematics of the Universe,
The University of Tokyo Institutes for Advanced Study,
The University of Tokyo
TEL: +81-04-7136-5980
E-mail: press@ipmu.jp


Research contacts

Surhud More
Project Assistant Professor
The Kavli Institute for the Physics and Mathematics of the Universe
TEL (office): +81-04-7136-6566
E-mail: surhud.moreAipmu.jp