Friday, February 25, 2011

Subaru Telescope Discovers A Rosetta Stone Cluster of Galaxies

Figure 1: The 4C 23.56 protocluster area. The red squares show objects (color-coded in green) that emit H-alpha emission lines. The field of view is 3.0 arcminutes by 3.7 arcminutes.

Parameters of this observation:
Telescope: Subaru Telescope (effective aperture 8.2 m)
Focus: Cassegrain
Instrument: MOIRCS (Multi-Object Infrared Camera and Spectrograph)
Filters: J band (1.26 micron), narrow band NB2288 (2.29 micron), Ks band (2.15 micron)
Dates in UT: June 2, 2007; August 23, 2008; September 19, 2008, and October 15, 2010
Exposure time: 45 minutes in J band, 46 minutes in Ks band, 2.3 hours in NB2288 band.
Orientation of the picture: north is up, and east is left.
Coordinates: Right Ascension (J2000.0) = 21 h 7.3 m, Declination (J2000.0) = +23 d 29.8 m (toward the constellation Vulpecula)

Figure 2: Close-up of a group of H-alpha-emitting galaxies located at the top left of Figure 1. The animation shows H-alpha emitting galaxies, alternating between the Ks (continuum) and H-alpha emissions. The circled objects are brighter in the line emissions.

Figure 3: Image of 4C 23.56 protocluster of galaxies in Spitzer Space Telescope observation. The background picture shows a reversed black-white image of mid-infrared emissions (24 micron). The bright objects display a lot of dust as well as active star formation. The black contour lines indicate the density of objects contained within them; they show good alignment with the H-alpha emitting objects (circled in red) detected by Subaru Telescope. The red square shows the area of MOIRCS observations. The image is Figure 9 in Tanaka, I., et al. 2011, PASJ, 63s2, and is reproduced with permission from the PASJ Editorial Office.

An international team of researchers led by Ichi Tanaka from the National Astronomical Observatory of Japan (NAOJ) has discovered an aggregate of galaxies undergoing a burst of star formation that may hold the key to understanding how galaxies formed in the early universe. The aggregate is located toward the Constellation Vulpecula and is 11 billion light years away (redshift z = 2.5), 2.7 billion years after the birth of the universe, when it was still in its infancy. These baby-booming galaxies may be a proto-cluster, an ancestor of present-day clusters of galaxies; they still seem to be growing into full-size galaxies. The discovery is the product of observations in 2007 with the Multi-Object Infrared Camera and Spectrograph (MOIRCS) on the Subaru Telescope and later observations with the Spitzer Telescope. By analyzing near-infrared emission data from the Subaru Telescope with mid-infrared emission data from the Spitzer Telescope, the current research team was able to identify the bright objects in the infrared as members of a primordial cluster. This accomplishment shows how the feedback between archived data, technology, and collaboration can produce continuing breakthroughs in our knowledge of the universe.

The Quest to Understand How the Earliest Galaxies Formed

Astronomers interested in understanding how galaxies evolved after the Big Bang, 13.7 billion years ago, search for that place in time when the transition from chaos to structure occurred—a celestial "Rosetta Stone" era that can clarify how early galaxies developed. They speculate that the transition to galactic structures probably occurred between ten and eleven billion years ago. Images of galaxies during this period can provide a basis for understanding the formation of galaxies. However, observation of such distant objects is difficult.

Measurements of Star Formation Rates as Clues for Finding Ancient Galaxies

Although current telescopes may capture faint images of ancient galaxies, scientists need more evidence to confirm and identify the nature of the objects in these images. The star formation rate (SFR) is one of the fundamental criteria that astronomers seek to establish in their search for ancient galaxies, because the SFR was likely to be quite high during galaxy formation.

Spectroscopic analysis of the signatures of an object's light can provide an estimate of SFR. H-alpha emission lines are one of the most popular signature lines that astronomers use to approximate SFR; they measure ionized hydrogen in the visible (optical) part of the spectrum.
However, atmospheric emissions begin to restrict measurements with H-alpha lines to a redshift of 2.7 (z = 2.7), a distance of about 11.2 billion light years away. The further the target galaxy is, the longer the wavelength of the spectral lines becomes; this is called the "redshift effect." A ground-based telescope cannot overcome this z = 2.7 boundary.

The Path to Discovery

Nevertheless, the current team was able to identify a primordial galaxy about 11 billion light years away. They overcame limitations in measuring features of far-distant objects by analyzing emission data from observations of the same area with two different telescopes at two different times.

In 2007, Subaru astronomer Ichi Tanaka used the Subaru Telescope to direct observations toward the area 4C 23.56, one of the more promising areas for proto-cluster candidates. The Subaru Telescope was mounted with MOIRCS and used a narrow band (NB) filter for detecting H-alpha lines at specific distances. The observations yielded data about the area that would become one piece of the solution to identifying the objects in the observations.

The tipping point for completing the discovery of the primordial galaxy came in the summer of 2010, when Tanaka was a resident at the European Southern Observatory (ESO) Some of Tanaka's colleagues were studying distant galaxies and analyzing archived data from the Spitzer Space Telescope when they noticed the presence of objects with faint mid-infrared emissions around 4C 23.56. Subsequent discussions with the European astronomers highlighted the meaning and significance of the connection between the near-infrared H-alpha emission lines obtained from the ground-based Subaru Telescope with the mid-infrared emissions from the Spitzer Space Telescope. Analysis of the two data sets from the ground-based Subaru Telescope and the Spitzer Space Telescope produced a powerful set of findings.

The Subaru observations with MOIRCS and a narrow band filter yielded a significant array of near-infrared emission-line objects around 4C 23.56. Although Subaru's H-alpha data alone was not sufficient to establish a high star formation rate, its link with Spitzer's mid-infrared data was. In addition, comparison of the star-formation rates in this area with those in another or in the general field show a clear difference in their star-forming activities. The area around 4C 23.56 at a redshift of z = 2.48 indicates that the team discovered a cluster of galaxies during an epoch of major star formation.

The discovery even surprised the researchers. Tanaka enthusiastically reflected about the breakthrough: "These primordial galaxies show a very high star formation rate, corresponding to the creation of about several hundreds of Suns per year. Such high star formation rates do not occur in any nearby galaxies, including the Milky Way. In addition, the number of mid-infrared sources apparently exceeds the amount that can be attributed to the objects visible in H-alpha emission. This indicates that there could be more dust-enshrouded galaxies with active star formation, invisible as H-alpha emissions but detectable in the mid-infrared."

Although clusters of galaxies in the universe form large and complicated networks, there are only a handful proto-clusters known to belong "Rosetta Stone" era. The cluster of galaxies discovered in the current observation is at z = 2.5. This is the furthest known primordial cluster of galaxies that comes within the H-alpha observable range with a ground-based telescope.

The current research team hopes to expand their efforts to locate and decode more Rosetta Stone galaxies by using the Subaru Telescope and the Atacama Large Millimeter Array (ALMA), a sub-millimeter interferometer to be commissioned soon.

Thursday, February 24, 2011

Planet Formation in Action?

PR Image eso1106a
Artist’s impression of the disc around the young star T Cha

PR Image eso1106b
The young star T Cha in the constellation of Chamaeleon

PR Image eso1106c
PR Image eso1106d
A Wide-field view of the sky around the young star T Cha (annotated)

PR Video eso1106a
Flying around the young star T Cha (artist's impression)

PR Video eso1106b
Zooming into the star T Cha

Astronomers may have found the first object clearing its path in the natal disc surrounding a young star

Using ESO’s Very Large Telescope an international team of astronomers has been able to study the short-lived disc of material around a young star that is in the early stages of making a planetary system. For the first time a smaller companion could be detected that may be the cause of the large gap found in the disc. Future observations will determine whether this companion is a planet or a brown dwarf.

Planets form from the discs of material around young stars, but the transition from dust disc to planetary system is rapid and few objects are caught during this phase [1]. One such object is T Chamaeleontis (T Cha), a faint star in the small southern constellation of Chamaeleon that is comparable to the Sun, but very near the beginning of its life [2]. T Cha lies about 350 light-years from the Earth and is only about seven million years old. Up to now no forming planets have been found in these transitional discs, although planets in more mature discs have been seen before (eso0842, heic0821).

“Earlier studies had shown that T Cha was an excellent target for studying how planetary systems form,” notes Johan Olofsson (Max Planck Institute for Astronomy, Heidelberg, Germany), one of the lead authors of two papers in the journal Astronomy & Astrophysics that describe the new work. “But this star is quite distant and the full power of the Very Large Telescope Interferometer (VLTI) was needed to resolve very fine details and see what is going on in the dust disc.”

The astronomers first observed T Cha using the AMBER instrument and the VLT Interferometer (VLTI) [3]. They found that some of the disc material formed a narrow dusty ring only about 20 million kilometres from the star. Beyond this inner disc, they found a region devoid of dust with the outer part of the disc stretching out into regions beyond about 1.1 billion kilometres from the star.

Nuria Huélamo (Centro de Astrobiología, ESAC, Spain), the lead author of the second paper takes up the story: “For us the gap in the dust disc around T Cha was a smoking gun, and we asked ourselves: could we be witnessing a companion digging a gap inside its protoplanetary disc?”

However, finding a faint companion so close to a bright star is a huge challenge and the team had to use the VLT instrument NACO in a novel and powerful way, called sparse aperture masking, to reach their goal [4]. After careful analysis they found the clear signature of an object located within the gap in the dust disc, about one billion kilometres from the star — slightly further out than Jupiter is within our Solar System and close to the outer edge of the gap. This is the first detection of an object much smaller than a star within a gap in the planet-forming dust disc around a young star. The evidence suggests that the companion object cannot be a normal star [5] but it could be either a brown dwarf [6] surrounded by dust or, most excitingly, a recently formed planet.

Huélamo concludes: “This is a remarkable joint study that combines two different state-of-the-art instruments at ESO’s Paranal Observatory. Future observations will allow us to find out more about the companion and the disc, and also understand what fuels the inner dusty disc.”

Notes

[1] The transitional discs can be spotted because they give off less radiation at mid-infrared wavelengths. The clearing of the dust close to the star and the creation of gaps and holes can explain this missing radiation. Recently formed planets may have created these gaps, although there are also other possibilities.

[2] T Cha is a T Tauri star, a very young star that is still contracting towards the main sequence.

[3] The astronomers used the AMBER instrument (Astronomical Multi-BEam combineR) and the VLTI to combine the light from all four of the 8.2-metre VLT Unit Telescopes and create a “virtual telescope” 130 metres across.

[4] NACO (or NAOS–CONICA in full) is an adaptive optics instrument attached to ESO’s Very Large Telescope. Thanks to adaptive optics, astronomers can remove most of the blurring effect of the atmosphere and obtain very sharp images. The team used NACO in a novel way, called sparse aperture masking (SAM) to search for the companion. This is a type of interferometry that, rather than combining the light from multiple telescopes as the VLTI does, uses different parts of the mirror of a single telescope (in this case, the mirror of the VLT Unit Telescope 4). This new technique is particularly good for finding faint objects very close to bright ones. VLTI/AMBER is better suited to studying the structure of the inner disc and is less sensitive to the presence of a distant companion.

[5] The astronomers searched for the companion using NACO in two different spectral bands — at around 2.2 microns and at 3.8 microns. The companion is only seen at the longer wavelength, which means that the object is either cool, like a planet, or a dust-shrouded brown dwarf.

[6] Brown dwarfs are objects between stars and planets in size. They are not massive enough to fuse hydrogen in their cores but are larger than giant planets such as Jupiter.

More information

This research was presented in two papers: Olofsson et al. 2011, “Warm dust resolved in the cold disk around TCha with VLTI/AMBER”, and Huélamo et al. 2011, “A companion candidate in the gap of the T Cha transitional disk”, to appear in the journal Astronomy & Astrophysics.

The team is composed of J. Olofsson (Max-Planck-Institut für Astronomie [MPIA], Heidelberg, Germany), M. Benisty (MPIA), J.-C. Augereau (Institut de Planétologie et d’Astrophysique de Grenoble [IPAG], France) C. Pinte (IPAG), F. Ménard (IPAG), E. Tatulli (IPAG), J.-P. Berger (ESO, Santiago, Chile), F. Malbet (IPAG), B. Merín (Herschel Science Centre, Madrid, Spain), E. F. van Dishoeck (Leiden University, Holland), S. Lacour (Observatoire de Paris, France), K. M. Pontoppidan (California Institute of Technology, USA), J.-L. Monin (IPAG), J. M. Brown (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany), G. A. Blake (California Institute of Technology), N. Huélamo (Centro de Astrobiología, ESAC, Spain), P. Tuthill (University of Sydney, Australia), M. Ireland (University of Sydney), A. Kraus (University of Hawaii) and G. Chauvin (Université Joseph Fourier, Grenoble, France).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links
Research papers (Olofsson, J. et. al., Huélamo, N. et. al.)
Photos of the VLT

Contacts

Dr. Nuria Huélamo
LAEFF-Center of Astrobiology - ESAC campus
Madrid, Spain
Tel: +34 91 813 1234
Email: nhuelamo@cab.inta-csic.es

Dr. Johan Olofsson
Max Planck Institute for Astronomy
Heidelberg, Germany
Tel: +49 6221 528 353
Email: olofsson@mpia.de

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 151 1537 3591
Email: rhook@eso.org

NGC 1999: South of Orion

NGC 1999

Explanation: South of the large star-forming region known as the Orion Nebula, lies bright blue reflection nebula NGC 1999. Also at the edge of the Orion molecular cloud complex some 1,500 light-years distant, NGC 1999's illumination is provided by the embedded variable star V380 Orionis.

The nebula is marked with a dark sideways T-shape near center in this broad cosmic vista that spans over 10 light-years.

The dark shape was once assumed to be an obscuring dust cloud seen in silhouette against the bright reflection nebula. But recent infrared images indicate the shape is likely a hole blown through the nebula itself by energetic young stars.

In fact, this region abounds with energetic young stars producing jets and outflows that create luminous shock waves. Cataloged as Herbig-Haro (HH) objects, named for astronomers George Herbig and Guillermo Haro, the shocks appear bright red in this view that includes HH1 and HH2 just below NGC 1999. The stellar jets and outflows push through the surrounding material at speeds of hundreds of kilometers per second.

Wednesday, February 23, 2011

Cassiopeia A: A supernova remnant about 11,000 light years away

Cassiopeia A (Cas A)
Credit X-ray: NASA/CXC/xx; Optical: NASA/STScI;
Illustration: NASA/CXC/M.Weiss



This composite image shows a beautiful X-ray and optical view of Cassiopeia A (Cas A), a supernova remnant located in our Galaxy about 11,000 light years away.
These are the remains of a massive star that exploded about 330 years ago, as measured in Earth's time frame. X-rays from Chandra are shown in red, green and blue along with optical data from Hubble in gold.

At the center of the image is a neutron star, an ultra-dense star created by the supernova. Ten years of observations with Chandra have revealed a 4% decline in the temperature of this neutron star, an unexpectedly rapid cooling. Two new papers by independent research teams show that this cooling is likely caused by a neutron superfluid forming in its central regions, the first direct evidence for this bizarre state of matter in the core of a neutron star.

The inset shows an artist's impression of the neutron star at the center of Cas A. The different colored layers in the cutout region show the crust (orange), the core (red), where densities are much higher, and the part of the core where the neutrons are thought to be in a superfluid state (inner red ball). The blue rays emanating from the center of the star represent the copious numbers of neutrinos -- nearly massless, weakly interacting particles -- that are created as the core temperature falls below a critical level and a neutron superfluid is formed, a process that began about 100 years ago as observed from Earth. These neutrinos escape from the star, taking energy with them and causing the star to cool much more rapidly.

This new research has allowed the teams to place the first observational constraints on a range of properties of superfluid material in neutron stars. The critical temperature was constrained to between one half a billion to just under a billion degrees Celsius. A wide region of the neutron star is expected to be forming a neutron superfluid as observed now, and to fully explain the rapid cooling, the protons in the neutron star must have formed a superfluid even earlier after the explosion. Because they are charged particles, the protons also form a superconductor.

Using a model that has been constrained by the Chandra observations, the future behavior of the neutron star has been predicted . The rapid cooling is expected to continue for a few decades and then it should slow down.

Fast Facts for Cassiopeia A:

Scale: Image is 8.91 arcmin across
Category: Supernovas & Supernova Remnants
Coordinates: (J2000) RA 23h 23m 26.7s | Dec +58° 49' 03.00"
Constellation: Cassiopeia
Observation Date: Nine observations in 2004: Feb 8, Apr 14, 18, 20, 22, 25 28, May 01, 05
Observation Time: 278 hours
Obs. ID: 4634-4639, 5196, 5319-5320
Color Code: X-ray: Red 0.5-1.5 keV; Green 1.5-2.5; Blue 4.0-6.0, Optical: Gold
Instrument: ACIS
Also Known As: Cas A
Distance Estimate: 10,000 light years

Quasar's Belch Solves Longstanding Mystery

Artist’s conceptualization of the environment around the supermassive black hole at the center of Mrk 231. The broad outflow seen in the Gemini data is shown as the fan-shaped wedge at the top of the accretion disk around the black hole. This side-view is not what is seen from the Earth where we see it ‘looking down the throat’ of the outflow. A similar outflow is probably present under the disk as well and is hinted at in this illustration. The total amount of material entrained in the broad flow is at least 400 times the mass of the Sun per year. Note that a more localized, narrower jet is shown, this jet was known prior to the Gemini discovery of the broader outflow featured here. Credit:Gemini Observatory/AURA, artwork by Lynette Cook - Download JPG 119 KB | TIFF 25.3 MB

When two galaxies merge to form a giant, the central supermassive black hole in the new galaxy develops an insatiable appetite. However, this ferocious appetite is unsustainable.

For the first time, observations with the Gemini Observatory clearly reveal an extreme, large-scale galactic outflow that brings the cosmic dinner to a halt. The outflow is effectively blowing the galaxy apart in a negative feedback loop, depriving the galaxy’s monstrous black hole of the gas and dust it needs to sustain its frenetic growth. It also limits the material available for the galaxy to make new generations of stars.

The groundbreaking work is a collaboration between David Rupke of Rhodes College in Tennessee and the University of Maryland’s Sylvain Veilleux. The results are to be published in the March 10 issue of The Astrophysical Journal Letters and were completed with support from the U.S. National Science Foundation.

According to Veilleux, Markarian 231 (Mrk 231), the galaxy observed with Gemini, is an ideal laboratory for studying outflows caused by feedback from supermassive black holes. “This object is arguably the closest and best example that we know of a big galaxy in the final stages of a violent merger and in the process of shedding its cocoon and revealing a very energetic central quasar. This is really a last gasp of this galaxy; the black hole is belching its next meals into oblivion!” As extreme as Mrk 231’s eating habits appear, Veilleux adds that they are probably not unique, “When we look deep into space and back in time, quasars like this one are seen in large numbers and all of them may have gone through shedding events like the one we are witnessing in Mrk 231.”

The environment around such a black hole is commonly known as an active galactic nucleus (AGN), and the extreme influx of material into these black holes is the power source for quasi-stellar objects or quasars. Merging galaxies help to feed the central black hole and also shroud it in gas. Mrk 231 is in transition, now clearing its surroundings. Eventually, running out of fuel, the AGN will become extinct. Without gas to form new stars, the host galaxy also starves to death, turning into a collection of old aging stars with few young stars to regenerate the stellar population. Ultimately, these old stars will make the galaxy appear redder giving these galaxies the moniker “red and dead.”

Although Mrk 231 is extremely well studied, and known for its collimated jets, the Gemini observations exposed a broad outflow extending in all directions for at least 8,000 light years around the galaxy’s core. The resulting data reveal gas (characterized by sodium, which absorbs yellow light) streaming away from the galaxy center at speeds of over 1,000 kilometers per second. At this speed, the gas could go from New York to Los Angeles in about 4 seconds. This outflow is removing gas from the nucleus at a prodigious rate – more than 2.5 times the star formation rate. The speeds observed eliminate stars as the possible “engine” fueling the outflow. This leaves the black hole itself as the most likely culprit, and it can easily account for the tremendous energy required.

The energy involved is sufficient to sweep away matter from the galaxy. However, "when we say the galaxy is being blown apart, we are only referring to the gas and dust in the galaxy,” notes Rupke. “The galaxy is mostly stars at this stage in its life, and the outflow has no effect on them. The crucial thing is that the fireworks of new star formation and black hole feeding are coming to an end, most likely as a result of this outflow.”

The environment around such a black hole is commonly known as an active galactic nucleus (AGN), and the extreme influx of material into these black holes is the power source for quasi-stellar objects or quasars. Merging galaxies help to feed the central black hole and also shroud it in gas. Mrk 231 is in transition, now clearing its surroundings. Eventually, running out of fuel, the AGN will become extinct. Without gas to form new stars, the host galaxy also starves to death, turning into a collection of old aging stars with few young stars to regenerate the stellar population. Ultimately, these old stars will make the galaxy appear redder giving these galaxies the moniker “red and dead.”

Numerical astrophysicist Philip Hopkins, a Miller Fellow at the University of California at Berkeley, explains that many physical processes unique to rapidly growing black holes are likely to play a role in propelling the winds observed by Gemini. “At its peak, the quasar shines with such intensity that the light itself is ‘trapped’ by a cocoon of gas and dust pushing on material with a force that can easily overcome the gravitational pull of the black hole.” Hopkins adds that the bath of X-rays and gamma rays known to be generated by quasars could also heat up the gas in the galaxy’s center until it reaches a temperature where it "boils over" and causes a bomb-like explosion. “But until now, we haven’t been able to catch a system ‘in the act.’” Part of the problem, according to Hopkins, has been that the most visible outflows are those ‘collimated jets’ already known in Mrk 231. These jets are trapped (probably by magnetic fields) in an extremely narrow beam, whereas material is falling into the black hole from all directions. The previously known jets therefore only cause very localized damage – drilling a tiny hole in the cocoon, rather than sweeping it away more broadly as seen in these new, more all-encompassing, outflows.

The observations for this study were obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini North, on Mauna Kea, Hawai‘i. The study used a powerful technique known as integral field spectroscopy. The integral field unit (IFU) in GMOS obtains a spectrum at several hundred points around the galaxy’s core. Each spectrum is then, in turn, used to determine the velocity of the gas at that point and represents the third dimension in what is called a data cube.

Markarian 231 is located about 600 million light years away in the direction of the constellation of Ursa Major. Although its mass is uncertain, some estimates indicate that Mrk 231 has a mass in stars about three times that of our Milky Way galaxy and its central black hole is estimated to have a mass of at least ten million solar masses or also about three times that of the supermassive black hole in the Milky Way.

Movie showing the gas in a galaxy merger with a quasar-driven “blowout”: https://www.cfa.harvard.edu/~phopkins/Site/Movies_files/collision_BH_run4.avi and: https://www.cfa.harvard.edu/~phopkins/Site/Movies.html


Background Information:

The growth of supermassive black holes, which are found in the centers of all normal galaxies (including our Milky Way), is fundamentally linked to the stars in galaxies. Black holes grow and stars form over time, resulting in a tight connection between the mass of the central black hole and the mass in stars of the host galaxy. Since most galaxies in the local universe do not currently have actively growing black holes at their centers, some process must eventually emerge to shut down this growth and development. Theoretical modeling specifically points to quasar outflows as the culprit. In this negative feedback loop, while the black hole is actively acquiring mass as a quasar, the outflows carry away energy and material, suppressing further growth. Small-scale outflows had been observed before, but none sufficiently powerful to account for this predicted and fundamental aspect of galaxy evolution. The Gemini observations provide the first clear evidence for outflows powerful enough to support the process necessary to starve the galactic black hole and quench star formation.



This extraction from the data cube shows the large-scale, fast outflow of neutral sodium at the center of the quasar Markarian 231. We are looking down onto the material that moves toward us relative to the galaxy, so the measured velocities are negative. The large black circle marks the location of the black hole, and red lines show the location of a radio jet. In addition to the quasar outflow, the jet pushes the material at the top right, resulting in even greater speeds. Part of the starburst is located at the position of the box at the lower left, and it is likely responsible for the gas motion in this region.

Science Contacts

David S.N. Rupke
Assistant Professor
Rhodes College, Dept. of Physics
Email: rupked@rhodes.edu
Phone: (901) 843-3914

Sylvain Veilleux
Professor
University of Maryland, Department of Astronomy
Email: veilleux@astro.umd.edu
Desk: (301) 405-0282
Cell: (240) 281-8372

Media Contacts:

Peter Michaud
Public Information and Outreach Manager
Gemini Observatory, Hilo, HI
Email: pmichaud@gemini.edu
Desk: (808) 974-2510
Cell: (808) 936-6643

Lee Tune
Associate Director, University Communications
University of Maryland
Email: ltune@umd.edu
Desk: (301) 405-4679

Monday, February 21, 2011

The Cigar Galaxy

This image of the Cigar Galaxy, Messier 82 (M82) or NGC 3034, was obtained using ACAM on the William Herschel Telescope. It is a colour composite made from data collected using red (including hydrogen alpha), green and blue filters. Credit: Pablo Rodríguez-Gil (IAC) y Pablo Bonet (IAC) [ JPEG | PDF (with text) ].

M82 is an irregular prototype starburst galaxy, whose centre is believed to be experiencing an episode of intense star formation. The red glow is from a superwind of ionised hydrogen gas, expanding out from the centre as a result of the combined winds of many individual stars.

ACAM instrument is a versatile optical imager and low-resolution spectrograph designed and built by ING. It is permanently mounted at a folded-Cassegrain focus of the William Herschel Telescope, adding more flexibility to the observational operation of the telescope. More information can be found at the ACAM home page.

Javier Méndez

Public Relations Officer
The Isaac Newton Group of Telescopes

Saturday, February 19, 2011

A Galactic Petri Dish

Abell 226
Credit:ESO


This rich scattering of galaxies was captured using the Wide Field Imager attached to the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. The thousands of galaxies contained in this small area of sky give a glimpse into the Universe’s distant past, whilst also acting as a powerful reminder of the immense scale of the cosmos.

This image was taken as part of the COMBO-17 project (Classifying Objects by Medium-Band Observations in 17 Filters), in which detailed surveys of five small patches of sky were made through 17 different coloured filters. The area of sky covered by each of the five regions is about the same area as that covered by the full Moon. The survey has produced a remarkable haul of celestial specimens. For example, across just three of these regions over 25 000 galaxies have been identified.

Just below the bright stars in the centre of the image is the galaxy cluster Abell 226. It was first noted by astronomer George Ogden Abell in his catalogue of galaxy clusters of 1958. The galaxies in Abell’s clusters, including Abell 226, are only up to a few billion light-years away. But behind these objects, even fainter, more distant galaxies were hiding.

The COMBO-17 study has unveiled these hidden galaxies, thanks to long exposure images from the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. Some of the most distant flecks of light visible in this photo represent galaxies whose light has been travelling towards us for about nine or ten billion years. That means that the galaxies in this image have a great variety of ages, some of them are quite similar to the Milky Way, while others reveal what the Universe was like when it was much younger.

This image was taken using three of the 17 filters from the study: B (in blue), V (in green), and R (in red).

Links
COMBO-17 at the Max Planck Institute for Astronomy

Thursday, February 17, 2011

'X-Class' Solar Flare from Jupiter-Sized Sun Spot Jams Radio, Satellite Signals: NASA


The strongest solar flare in four years disrupted radio communications in southern China, according to the China Meteorological Administration. The powerful solar eruption triggered a huge geomagnetic storm has disturbed radio communications and could disrupt electrical power grids, radio and satellite communication in the next days, NASA said.

A strong wave of charged plasma particles emanating from the Jupiter-sized sun spot, the most powerful seen in four years, has already disrupted radio communication in southern China.
The Class X flash -- the largest such category -- erupted at 0156 GMT Tuesday, according to the US space agency.

"X-class flares are the most powerful of all solar events that can trigger radio blackouts and long-lasting radiation storms," disturbing telecommunications and electric grids, NASA said Wednesday. Geomagnetic storms usually last 24 to 48 hours, but some could last for many days, said the US National Weather Service.

"Ground to air, ship to shore, shortwave broadcast and amateur radio are vulnerable to disruption during geomagnetic storms. Navigation systems like GPS can also be adversely affected."
NASA's Solar Dynamics Observatory said it saw a large coronal mass ejection (CME) associated with the flash blasting toward Earth at about 560 miles per second (900 kilometers per second).
The flare spread from Active Region 1158 in the sun's southern hemisphere, which had so far lagged behind the northern hemisphere in flash activity. It followed several smaller flares in recent days.

"The calm before the storm," says the US National Weather Service Space Weather Prediction Service.

Direct Images of Disks Unravel Mystery of Planet Formation

Figure 1: Near-infrared (1.6 micron) images of AB Aur.

The top panels compare images taken by HiCIAO and CIAO. Both images have a field of view of 7.5" by 7.5". Top left: Image taken by HiCIAO using a coronagraphic occulting mask with a 0.3" diameter. Top right: Image taken by CIAO using a software mask with a 1.7” diameter. The bottom panels show close-up views of the inner part of AB Aur's disk. Both images have a field of view of 2.0” by 2.0". Bottom left: Image has a coronagraphic occulting mask with a 0.3" diameter.
Bottom right: Image includes labels of its prominent features. The central position (0, 0) refers to the location of the star. Ellipsoids in dashed lines show the outer and inner rings. The solid ellipsoid indicates the wide gap between the rings. The "+" shows where the star is. The filled circle is the center of the outer ring. For this object, 1" (one arc second) corresponds to 144 AU in real scale (144 times the distance between Earth and Sun). For high resolution versions of all of the above images, click anywhere on any of them. For a high resolution version of ONLY the bottom left image, click on the following links: image only or image with English label.



Figure 2: High-contrast near-infrared imaging of LkCa 15 disk.

Top: Image taken by HiCIAO. The central star is hidden by the dark brown area toward the center. The inner edge of the outer disk is visible. The white feature below the blocked out area is part of the disk illuminated by the central star. The opposite side of the disk is not readily visible. There is a gap between the inner boundary of the disk and the star, at a distance of about 50 AU (Astronomical Unit, the distance between the Earth and the Sun, about 150 million kilometers or 94 million miles. The middle figure is a sketch of the LkCa 15 star and its disk system. The yellow-colored region corresponds to the features in the HiCIAO image. Bottom: Neptune's orbit in the Solar System as a scale comparison.


Abstract

The fruits of the SEEDS (Strategic Explorations of Exoplanets and Disks with Subaru) Project, led by Motohide Tamura at NAOJ (National Astronomical Observatory of Japan), are accumulating. Composed of over 100 scientists and 25 institutions, the international consortium of researchers supporting the project has announced another set of stunning findings obtained with the recently commissioned Subaru instrument HiCIAO (High Contrast Instrument for the Subaru Next Generation Adaptive Optics), an upgraded version of its predecessor CIAO (Coronographic Imager with Adaptive Optics). Their initial announcement of a significant discovery came in December, 2009: an exoplanet candidate around a Sun-like star. Now they are announcing another remarkable discovery: direct and sharp images of the protoplanetary disks of two young stars that reveal how planets may have formed within them. No other telescopes, whether ground-based or in space, have ever penetrated so close to a central star, showing the details of its disk.

The Significance and Challenges of Research on Protoplanetary Disks

One key to understanding planetary formation lies in the protoplanetary disks of young stars, which provide the initial conditions for the development of planets. These flattened structures of dense gas and dust evolve as by-products of star formation and become the womb for the maturation of planets (Conventional Schematic Diagrams of the Evolution of a Protoplanetary Disk around a Sun-like Star). However, scientists have not determined the actual details of how planets originate and mature. The detection of over 500 exoplanets that orbit around stars outside of our solar system has heightened interest in disks as a source of planetary formation. Did planets grow from the collision of bodies of rock and/or ice (planetesimals) or from gravitational instability in their disks? How does the development of exoplanets help us explain how the Earth formed?

The answers are difficult to obtain because disks are challenging to study. Both the small angular size of disks as well as the apparent dimness of a disk relative to its bright central star pose barriers to detailed observations of disks. In addition, available spatial resolution has only permitted the study of the outer envelope of a disk's structure. Finally, the scale size for observations is much larger than the familiar scale of our solar system, a scale that even the highest resolution telescopes have had difficulty in accessing so far.

Specialized instruments help scientists meet these challenges. A coronagraph facilitates observation of dim objects around a star by masking its extremely bright light while adaptive optics (AO) enhance spatial resolution by compensating for the blurring effects of the Earth’s atmosphere.

Subaru Telescope has been in the forefront of developing instruments designed for planet-hunting. In late 2009 Subaru Telescope replaced its earlier coronograph CIAO with HiCIAO that features not only a 188-element AO system and a stellar coronograph thats block out the central star's light but also various advanced techniques to enhance observation of the fine features inside a disk.

The Strategic Approach of the SEEDS Project

The SEEDS Project uses HiCIAO's planet-hunting technology to study exoplanets and their processes of formation. Begun in 2009 and led by Motohide Tamura of NAOJ, the project is one of the first large-scale undertakings approved by Subaru to implement a strategic, coherent approach to exploring the universe with its telescope. The consortium of project supporters has grown to include an international group of scientists and institutions as well as a variety of experts, including those in the areas of data analysis and high resolution imaging.

The SEEDS Project’s New Discoveries about Protoplanetary Disks

The SEEDS' Project has yielded new discoveries about protoplanetary disks that contribute to our understanding of how planets may form. They focus on observations of two young stars.

Details of the Disk of AB Aur

One of the primary targets was the very young star AB Aur in the constellation Auriga ("the Charioteer"). It is only about one million years old and 460 light years away from Earth. The research group has succeeded in directly imaging the fine details of AB Aur's disk. This is the first, finest, and sharpest image of a disk ever taken for this or any other objects.

Figure 1 shows the recent images of AB Aur taken by HiCIAO compared with the image taken by CIAO in 2004. The HiCIAO images display high spatial resolution and high contrast that reveals fine details of the disk’s inner structure that are on a scale similar to Neptune’s orbit in our solar system. Such precision of features near its central star contrasts with their masking in the earlier CIAO image.

The bottom two images in Figure 1 show close-ups of the inner disk, displaying the richness of its features. Double rings with some intricate bright and dark patterns are readily visible; they are tilted relative to each other, and strangely, their centers do not coincide with the position of the central star. A gap between these rings is rather strikingly void of material.

The disk's irregularities point to the presence of a giant planet that may sweep up material between the rings and cause irregularities in them with its gravitational force. Unfortunately this planet is not visible because disk material still covers it, extinguishing the planet's light.

A Gap in the Disk of the Star LkCa 15

The research group also targeted the star LkCa 15 for an examination of its disk. The star LkCa 15 is located toward the constellation Taurus, has a weight similar to the Sun's, and is several million years old. Its disk has been observed for some time. Although spectral energy distributions have indicated a gap in the disk, no direct imaging has clearly confirmed the presence of the gap-until now. The SEEDS group used HiCIAO for their observations, which succeeded in capturing a high-resolution image of the LkCa 15 disk.

Figure 2 shows an image of the disk of LKCa 15, which is masked in the dark area. The faint feature below the masked star is part of the disk illuminated by the central star. The opposite segment of the disk is not visible. The void between these features is the gap between the disk and the central star, which has a scale similar to Neptune's orbit in our solar system. The lack of material in the vicinity of the central star implies that a giant planet is sweeping up the disk's leftover materials that the central star did not swallow. Although the image might seem a bit blurry to readers, this is the first clear example of a truncated structure of a protoplanetary disk.

Implications for Planet Formation

These two results are the first to show features within disks where the planets are actually being born, and on a scale similar to that of our solar system. The direct imaging strongly indicates the existence of Jupiter-like giant planets that have affected the structure of the disks. Theorists were surprised to discover planets already formed within one million years. They had thought that giant planets such as Jupiter and Saturn in our solar system as well as giant exoplanets would take several tens of million years to form. The findings from the current research give them a tighter boundary condition for developing a theory of planetary formation. And the SEEDS Project will continue to search for and study exoplanets over the next five years, contributing even more to solving the mysteries of planet formation.

This result has been published in the Astrophysical Journal (volume 729, page 17, 2011 March 10 issue)

Institutions and Institutional Affiliations of Researchers

National Astronomical Observatory of Japan, The Graduate University for Advanced Studies (SOKENDAI), Max Planck Institute for Astronomy (Germany), Hokkaido University, Tohoku University, Ibaraki University, Saitama University, The University of Tokyo, Tokyo Institute of Technology, Institute of Space and Astronautical Science/Japan Aerospace Exploration Agency, Kanagawa University, Nagoya University, Nagoya City University, Osaka University, Kobe University, The Open University of Japan, Princeton University, University of Hawaii, Jet Propulsion Laboratory, Academia Sinica Institute of Astronomy and Astrophysics ASIAA (Taiwan), University of Nice Sophia Antipolis (France), University of Hertfordshire (UK), Eureka Scientific and Goddard Space Flight Center, University of Washington, The College of Charleston.

Acknowledgment

This work is supported by a Grant-in-Aid for Specially Promoted Research from the Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT).

Hubble Shows New Image of Spiral Galaxy NGC 2841

Spiral Galaxy NGC 2841
Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Acknowledgment: M. Crockett and S. Kaviraj (Oxford University, UK), R. O'Connell (University of Virginia), B. Whitmore (STScI), and the WFC3 Scientific Oversight Committee

NASA's Hubble Space Telescope reveals a majestic disk of stars and dust lanes in this view of the spiral galaxy NGC 2841.

A bright cusp of starlight marks the galaxy's center. Spiraling outward are dust lanes that are silhouetted against the population of whitish middle-aged stars. Much younger blue stars trace the spiral arms.

Notably missing are pinkish emission nebulae indicative of new star birth. It is likely that the radiation and supersonic winds from fiery, super-hot, young blue stars cleared out the remaining gas (which glows pink), and hence shut down further star formation in the regions in which they were born. NGC 2841 currently has a relatively low star formation rate compared to other spirals that are ablaze with emission nebulae.

NGC 2841 lies 46 million light-years away in the constellation of Ursa Major (The Great Bear). This image was taken in 2010 through four different filters on Hubble's Wide Field Camera 3. Wavelengths range from ultraviolet light through visible light to near-infrared light.

Acknowledgment: M. Crockett and S. Kaviraj (Oxford University, UK), R. O'Connell (University of Virginia), B. Whitmore (STScI), and the WFC3 Scientific Oversight Committee.

Technical facts about this news release:

Object Name: NGC 2841
Object Description: Flocculent Spiral Galaxy
Position (J2000): R.A. 9h 22m 02.64s Dec. +50° 58' 35.47"
Constellation: Ursa Major
Distance: About 46 million light-years (14 million parsecs)
Dimensions: The image is 2.6 arcminutes (34,000 light-years or 10,500 parsecs) wide.

About the Data Data Description: The image was created from Hubble data from proposal 11360: R. O'Connell (University of Virginia), B. Balick (University of Washington), H. Bond (STScI), D. Calzetti (University of Massachusetts), M. Carollo (Swiss Federal Institute of Technology, Zurich), M. Disney (University of Wales, College of Cardiff), M. Dopita (Australian National University), J. Frogel (Ohio State University Research Foundation), D. Hall (University of Hawaii), J. Holtzman (New Mexico State University), P. McCarthy (Carnegie Institution of Washington), F. Paresce (European Southern Observatory, Germany), A. Saha (NOAO/AURA), J. Silk (University of Oxford), A. Walker (NOAO/CTIO), B. Whitmore (STScI), R. Windhorst (Arizona State University), and E. Young (University of Arizona).

Instrument: WFC3/UVIS
Exposure Date(s): January 5-7, 2010
Exposure Time: 2 hours
Filters: F336W (U), F547M (y), F657N (H-alpha + [N II]), and F814W (I)

Color: This image is a composite of separate exposures acquired by the WFC3 instrument on HST. Several filters were used to sample broad and narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are:
  • F336W (U) blue
  • F547M (y) green
  • F657N (H-alpha + [N II]) red-orange
  • F814W (I) red

Wednesday, February 16, 2011

Herschel finds less dark matter but more stars

The calculated distribution of dark matter
Credits: The Virgo Consortium/Alexandre Amblard/ESA

Hi-Res Jpeg (Size: 363 kb)

ESA’s Herschel space observatory has discovered a population of dust-enshrouded galaxies that do not need as much dark matter as previously thought to collect gas and burst into star formation.

The galaxies are far away and each boasts some 300 billion times the mass of the Sun. The size challenges current theory that predicts a galaxy has to be more than ten times larger, 5000 billion solar masses, to be able form large numbers of stars.

The new result is published today in a paper by Alexandre Amblard, University of California, Irvine, and colleagues.

Most of the mass of any galaxy is expected to be dark matter, a hypothetical substance that has yet to be detected but which astronomers believe must exist to provide sufficient gravity to prevent galaxies ripping themselves apart as they rotate.

Herschel's target: the so-called Lockman Hole
Credits: ESA & SPIRE consortium & HerMES consortium
Hi-Res Jpeg (Size: 1666 kb)

Current models of the birth of galaxies start with the accumulation of large amounts of dark matter. Its gravitational attraction drags in ordinary atoms. If enough atoms accumulate, a ‘starburst’ is ignited, in which stars form at rates 100–1000 times faster than in our own galaxy does today.

“Herschel is showing us that we don’t need quite so much dark matter as we thought to trigger a starburst,” says Asantha Cooray, University of California, Irvine, a co-author on today’s paper.

This discovery was made by analysing infrared images taken by Herschel’s SPIRE (Spectral and Photometric Imaging Receiver) instrument at wavelengths of 250, 350, and 500 microns. These are roughly 1000 times longer than the wavelengths visible to the human eye and reveal galaxies that are deeply enshrouded in dust.

“With its very high sensitivity to the far-infrared light emitted by these young, enshrouded starburst galaxies, Herschel allows us to peer deep into the Universe and to understand how galaxies form and evolve,” says Göran Pilbratt, the ESA Herschel project scientist.

There are so many galaxies in Herschel’s images that they overlap, creating a fog of infrared radiation known as the cosmic infrared background. The galaxies are not distributed randomly but follow the underlying pattern of dark matter in the Universe, and so the fog has a distinctive pattern of light and dark patches.

The calculated distribution of dark matter
Credits: The Virgo Consortium/Alexandre Amblard/ESA
Hi-Res Jpeg (Size: 1792 kb)

Analysis of the brightness of the patches in the SPIRE images has shown that the star-formation rate in the distant infrared galaxies is 3–5 times higher than previously inferred from visible-wavelength observations of similar, very young galaxies by the Hubble Space Telescope and other telescopes.

Further analysis and simulations have shown that this smaller mass for the galaxies is a sweet spot for star formation. Less massive galaxies find it hard to form more than a first generation of stars before fizzling out. At the other end of the scale, more massive galaxies struggle because their gas cools rather slowly, preventing it from collapsing down to the high densities needed to ignite star formation.

But at this newly identified ‘just-right’ mass of a few hundred billion solar masses, galaxies can make stars at prodigious rates and thus grow rapidly.

“This is the first direct observation of the preferred mass scale for igniting a starburst,” says Dr Cooray.

Models of galaxy formation can now be adjusted to reflect these new results, and astronomers can take a step closer to understanding how galaxies – including our own –came into being.

Contact for further information

Reflected Glory

PR Image eso1105a
Messier 78: a reflection nebula in Orion

PR Image eso1105b
Messier 78: a reflection nebula in Orion

PR Image eso1105c
Highlights of Messier 78: a reflection nebula in Orion

PR Image eso1105d
McNeil's Nebula in Messier 78

PR Video eso1105a
Zooming in on Messier 78

PR Video eso1105b
Panning across the reflection nebula Messier 78

The nebula Messier 78 takes centre stage in this image taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, while the stars powering the bright display take a backseat. The brilliant starlight ricochets off dust particles in the nebula, illuminating it with scattered blue light. Igor Chekalin was the overall winner of ESO’s Hidden Treasures 2010 astrophotography competition with his image of this stunning object.

Messier 78 is a fine example of a reflection nebula. The ultraviolet radiation from the stars that illuminate it is not intense enough to ionise the gas to make it glow — its dust particles simply reflect the starlight that falls on them. Despite this, Messier 78 can easily be observed with a small telescope, being one of the brightest reflection nebulae in the sky. It lies about 1350 light-years away in the constellation of Orion (The Hunter) and can be found northeast of the easternmost star of Orion’s belt.

This new image of Messier 78 from the MPG/ESO 2.2-metre telescope at the La Silla Observatory is based on data selected by Igor Chekalin in his winning entry to the Hidden Treasures competition [1].

The pale blue tint seen in the nebula in this picture is an accurate representation of its dominant colour. Blue hues are commonly seen in reflection nebulae because of the way the starlight is scattered by the tiny dust particles that they contain: the shorter wavelength of blue light is scattered more efficiently than the longer wavelength red light.

This image contains many other striking features apart from the glowing nebula. A thick band of obscuring dust stretches across the image from the upper left to the lower right, blocking the light from background stars. In the bottom right corner, many curious pink structures are also visible, which are created by jets of material being ejected from stars that have recently formed and are still buried deep in dust clouds.

Two bright stars, HD 38563A and HD 38563B, are the main powerhouses behind Messier 78. However, the nebula is home to many more stars, including a collection of about 45 low mass, young stars (less than 10 million years old) in which the cores are still too cool for hydrogen fusion to start, known as T Tauri stars. Studying T Tauri stars is important for understanding the early stages of star formation and how planetary systems are created.

Remarkably, this complex of nebulae has also changed significantly in the last ten years. In February 2004 the experienced amateur observer Jay McNeil took an image of this region with a 75 mm telescope and was surprised to see a bright nebula — the prominent fan shaped feature near the bottom of this picture — where nothing was seen on most earlier images. This object is now known as McNeil’s Nebula and it appears to be a highly variable reflection nebula around a young star.

This colour picture was created from many monochrome exposures taken through blue, yellow/green and red filters, supplemented by exposures through an H-alpha filter that shows light from glowing hydrogen gas. The total exposure times were 9, 9, 17.5 and 15.5 minutes per filter, respectively.
Notes

[1] Igor Chekalin from Russia uncovered the raw data for this image of Messier 78 in ESO’s archives in the competition Hidden Treasures (eso1102). He processed the raw data with great skill, claiming first prize in the contest for his final image (Flickr link). ESO’s team of in-house image processing experts then independently processed the raw data at full resolution to produce the image shown here.
More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Photo of MPG/ESO 2.2-metre telescope
Photos of La Silla Observatory

Contacts

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Tuesday, February 15, 2011

Isolating a thick disc in Andromeda

Schematic representation of a thick disc structure. The thick disc is formed of stars that are typically much older than those in the thin disc, making it an ideal probe of galactic evolution . Credit: Amanda Smith, IoA graphics officer

A team of astronomers from the UK, the US and Europe have identified a thick stellar disc in the nearby Andromeda galaxy for the first time. The discovery and properties of the thick disc will constrain the dominant physical processes involved in the formation and evolution of large spiral galaxies like our own Milky Way.

By analysing precise measurements of the velocities of individual bright stars within the Andromeda galaxy using the Keck telescope in Hawaii, the team have managed to separate out stars tracing out a thick disc from those comprising the thin disc, and assess how they differ in height, width and chemistry.

Optical image of The Andromeda galaxy (M31)
Credit: Robert Gendler


Spiral structure dominates the morphology of large galaxies at the present time, with roughly 70% of all stars contained in a flat stellar disc. The disc structure contains the spiral arms traced by regions of active star formation, and surrounds a central bulge of old stars at the core of the galaxy. “From observations of our own Milky Way and other nearby spirals, we know that these galaxies typically possess two stellar discs, both a ‘thin’ and a ‘thick’ disc,” explains the leader of the study, Michelle Collins, a PhD student at Cambridge’s Institute of Astronomy. The thick disc consists of older stars whose orbits take them along a path that extends both above and below the more regular thin disc. “The classical thin stellar discs that we typically see in Hubble imaging result from the accretion of gas towards the end of a galaxy’s formation, whereas thick discs are produced in a much earlier phase of the galaxy’s life, making them ideal tracers of the processes involved in galactic evolution.”

Currently, the formation process of the thick disc is not well understood. Previously, the best hope for comprehending this structure was by studying the thick disc of our own Galaxy, but much of this is obscured from our view. The discovery of a similar thick disk in Andromeda presents a much cleaner view of spiral structure. Andromeda is our nearest large spiral neighbour -- close enough to be visible to the unaided eye -- and can be seen in its entirety from the Milky Way. Astronomers will be able to determine the properties of the disk across the full extent of the galaxy and look for signatures of the events connected to its formation. It requires a huge amount of energy to stir up a galaxy's stars to form a thick disc component, and theoretical models proposed include accretion of smaller satellite galaxies, or more subtle and continuous heating of stars within the galaxy by spiral arms.

Ages and orientations of the stellar components of disc galaxies. The halo (or spheroid) contains the oldest populations, followed by the thick stellar disc. The thin disc typically contains the youngest generations of stars. Credit: RAVE collaboration

"Our initial study of this component already suggests that it is likely older than the thin disc, with a different chemical composition'' commented UCLA Astronomer, Mike Rich, "Future more detailed observations should enable us to unravel the formation of the disc system in Andromeda, with the potential to apply this understanding to the formation of spiral galaxies throughout the Universe.''

"This result is one of the most exciting to emerge from the larger parent survey of the motions and chemistry of stars in the outskirts of Andromeda,'' said fellow team member, Dr. Scott Chapman, also at the Institute of Astronomy. "Finding this thick disc has afforded us a unique and spectacular view of the formation of the Andromeda system, and will undoubtedly assist in our understanding of this complex process.''

This study was published in Monthly Notices of the Royal Astronomical Society (see the accepted paper) by Michelle Collins, Scott Chapman and Mike Irwin from the Institute of Astronomy, together with Rodrigo Ibata from L'Observatoire de Strasbourg, Mike Rich from University of California, Los Angeles, Annette Ferguson from the Institute for Astronomy in Edinburgh, Geraint Lewis from the University of Sydney, and Nial Tanvir and Andreas Koch from the University of Leicester.

This study is published in Monthly Notices of the Royal Astronomical Society:
http://arxiv.org/abs/1010.5276
http://www.ast.cam.ac.uk/~mlmc2/M31thickdisc.html

Caught in the act: sneak preview of galaxy cluster that’s still forming

Region around starburst galaxy COSMOS AzTEC-3. The green circle is 13 million light years across. Credit: Capak et al. / Nature

Astronomers have found a “protocluster” that was around only 1 billion years after the Big Bang (that’s a redshift of 5.3 for anyone that’s counting). It sits in a region that is 40 million light years across and is rich in young stars.

The protocluster was found in data from the Cosmological Evolution Survey, COSMOS. COSMOS uses the Hubble, Spitzer and Chandra space telescopes with the ground based Keck Observatory and Japan’s Subaru Telescope to get an good look at the universe. COSMOS looks at a tiny region of space — about 0.005% of the whole sky, or two square degrees — in all wavelengths of light, from radio to gamma waves.

Peter Capak, the lead author on the paper published in Nature last week, and colleagues knew that extremely bright objects such as starburst galaxies (galaxies with an unusually high amount of star formation) and quasars (the bit at the centre of a massive galaxy that surrounds the supermassive black hole) should exist in very young galaxy clusters, so they first looked for objects giving off a lot of radiation. They found objects emitting a lot of visible light by measuring optical and near-infrared radiation, starburst galaxies by taking radio wave measurements and quasars using X-rays. Once they had located these extreme objects, they looked in the areas surrounding them for unusually large numbers of galaxies given the size of the area — something they called “overdensities”. They then used Hubble and Subaru to measure how far away these extreme objects were, and the Keck II telescope in Hawaii to confirm the observations.

Capak and colleagues were particularly interested in an “overdensity” near a starburst galaxy known as COSMOS AzTEC-3. The area in question contained over 50 billion times the mass of the Sun in gas (and ten times more dark matter), and was brighter than 10 trillion Suns. Stars in the region are forming at a rate of over 1500 a year, more than a hundred times the average value.

Around COSMOS AzTEC-3 there were 11 bright galaxies — 10 more than would normally be expected. This led to the conclusion that what they were seeing was the beginnings of a galaxy cluster, known as a protocluster.

Chandra X-ray observations helped to pin down a quasar very close to the protocluster. It can be difficult to find quasars that are this far away because, although they are the most luminous objects in the universe, they’re not usually bright enough to be seen by the telescope. But this one was. The astronomers worked out that the quasar’s black hole must have a mass of between ten and a hundred million times the mass of the Sun.

Putting all of this information together, astronomers worked out the total mass of the protocluster. It weighs in at at least ten billion time the mass of the Sun, but could be up to a hundred billion Suns. This confirmed what the astronomers suspected: they were looking at one of the biggest and brightest objects at this distance.

Six of the 11 very bright objects in the protocluster. COSMOS AzTEC-3 is labelled "Starburst". Credit: Capak et al./Nature

Astronomers also measured the amount of gas in the protocluster. This is what will fuel the protocluster’s growth. They found more than enough to point to a very bright, and massive, future for the baby cluster. It will eventually evolve (or rather, confusingly, already has evolved — depending on which way you look at it) into a massive galaxy cluster. Massive clusters of galaxies have been found from around 4 billion years after the Big Bang, giving this one at least 3 billion years to grow up.

Reference

Capak PL, Riechers D, Scoville NZ, Carilli C, Cox P, Neri R, Robertson B, Salvato M, Schinnerer E, Yan L, Wilson GW, Yun M, Civano F, Elvis M, Karim A, Mobasher B, & Staguhn JG (2011). A massive protocluster of galaxies at a redshift of z ≈ 5.3. Nature, 470 (7333), 233-5 PMID: 21228776

It’s also on arXiv