Planck unveils the Universe - old and young

A false-colour image of the whole sky as seen by Planck. The dust throughout the Galaxy is shown in blue, while hot gas can be seen as red regions across the centre of the image. In the background, the mottled yellow features are relic radiation, called the Cosmic Microwave Background, which contains information about the earliest stages of the Universe. This image is a low-resolution version of the full data set. The areas of sky shown in previous releases are outlines and labelled. Image credit: ESA / LFI and HFI Consortia.

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Image credit: ESA / LFI and HFI Consortia

Image credit: ESA / LFI and HFI Consortia

Planck has delivered its first image of the entire sky. By looking at microwave radiation, it not only provides new insight into the way stars and galaxies form, but also tells us how the Universe itself came to life after the Big Bang.

Professor George Efstathiou, at University of Cambridge and the Planck Survey Scientist, said “it has taken sixteen years of hard work by many scientists in Europe, the USA and Canada, to produce this new image of the early Universe. Planck is working brilliantly and we expect to learn a lot about the Big Bang and the creation of our Universe.”

Dr David Parker, Director of Space Science and Exploration for the UK Space Agency, added, “Planck has ‘painted’ us its first spectacular picture of the Universe. This single image captures both our own cosmic backyard – the Milky Way galaxy that we live in – but also the subtle imprint of the Big Bang from which the whole Universe emerged. We’re proud to be supporting this great new discovery machine and look forward to our scientists unravelling the deeper meaning behind the beauty of this first image.”

From the closest portions of the Milky Way to the furthest reaches of space and time, the new all-sky Planck image is an extraordinary treasure chest of new data for astronomers. The main disc of our Galaxy runs across the centre of the image. Immediately striking are the streamers of cold dust reaching above and below the Milky Way. This galactic web is where new stars are being formed, and Planck has found many locations where individual stars are edging toward birth or just beginning their cycle of development.

Less spectacular but perhaps more intriguing is the mottled backdrop at the top and bottom. This is the cosmic microwave background (CMB) radiation. It is the oldest light in the Universe, the remains of the fireball out of which our Universe sprang into existence 13.7 billion years ago.

While the Milky Way shows us what our local neighbourhood looks like now, those microwaves show us what the Universe looked like close to its time of creation, before there were stars or galaxies. The CMB radiation was released as the first atoms were forming, about 400 000 years after the Big Bang, and is at the heart of Planck’s mission to decode what happened in the primordial Universe.

The microwave pattern is the cosmic blueprint from which today’s clusters of galaxies were built. The different colours represent minute differences in the temperature and density of matter across the sky. Through the action of gravity, these small irregularities evolved into denser regions that became the galaxies of today.

The CMB covers the entire sky but most of it is hidden in this image by the Milky Way’s emission, which must be digitally removed from the final data in order to see the microwave background in its entirety. Planck looks at the sky in nine different bands, or colours, of microwave light, which have wavelengths thousands of times that of optical light. These nine different bands, ranging from frequencies of 30 to 850 GHz, are crucial for understanding which parts of the Planck data are from the early Universe, and which are from our own Galaxy. Clive Dickinson, of the University of Manchester, said “Planck has the unique ability to distinguish very cold dust at temperatures of just a few degrees above absolute zero (-273.15oC) from the warmer dust at tens of degrees above absolute zero. These regions of space are likely to be where stars form, and Planck will allow us to study such regions over large regions of sky for the first time.”

A number of UK institutions have been involved in the design and construction of the satellite, and are now working alongside colleagues from around the world to operate the satellite and analyse the data. Dr David Clements, of Imperial College London, said “just looking at the pictures you can tell we're seeing new things about the structure of our galaxy. Once we've done that, and stripped away these foregrounds, then it's on to the Cosmic Microwave Background and the glow of the Big Bang itself!”

The image shown here is constructed from data taken from the first ten months of Planck’s main mission, with observations beginning in August 2009. Planck continues to map the Universe, and by the end of its mission in 2012 it will have imaged the whole sky four times. The first full data release of the CMB is planned for 2012. Before then, a catalogue containing individual objects, both regions in our Galaxy and entire distant galaxies, will be released in January 2011.

Professor Peter Ade, at Cardiff University, has been involved with design, construction and operation of the High Frequency Instrument. He said “at last we can see the realisation of the full potential of Planck, showing in exquisite detail our own Milky Way galaxy superimposed on the relic fireball background. It is a fantastic result for this unique satellite, and demonstrates once again that you can only do pioneering science by using advanced and therefore high risk technologies.”

The Jodrell Bank Centre for Astrophysics at the University of Manchester is involved with the Low Frequency Instrument. Rod Davies, Emeritus Professor at Jodrell, said “it is particularly rewarding for me to see the culmination of a 30-year involvement in Cosmic Microwave Background research beginning with radio telescopes at Jodrell Bank in Cheshire, then under the clear dry skies on the high volcanic slopes of Tenerife and finally with the construction by Jodrell Bank of the radio receivers for Planck’s Low Frequency Instrument.”

Herschel reveals details of distant galaxies and quasars

Image of the gravitational lens Abell 2218, as seen by Herschel. Click here, for more download options. Image credit: ESA/SPIRE and HerMES Consortia.

Amazing new data captured by ESA’s Herschel Space Observatory – carrying the largest mirror ever launched into space - have just been publicly released, allowing the World’s astronomers to share in the Herschel SPIRE instrument’s observations of distant galaxies. From its vantage point nearly 1.5 million km from Earth (1 million miles), the Herschel spacecraft has given astronomers new insights into the different types of galaxy in the distant Universe and will allow them to explore part of the Universe as it was some eleven billion years ago or just 3 billion years after the Big Bang.

Dr David Parker, Director of Space Science and Exploration for the UK Space Agency, said, “We’re very proud to be supporting this groundbreaking mission. Herschel is a key part of the UK Space Agency’s programme to explore the ancient Universe and understand how galaxies, stars and planets form. Herschel can see back in time because the light left the stars making up the distant galaxies billions of years before our planet Earth was formed and has been travelling through space ever since, only now to be captured by the spacecraft’s sensitive eyes. ”

The new data is part of the Herschel Multi-tiered Extragalactic Survey (HerMES), led by Professor Seb Oliver, University of Sussex, and Dr Jamie Bock, NASA Jet Propulsion Laboratory and California Institute of Technology. The HerMES data, now publicly released, has already helped to confirm the relationship between super-massive black holes and the galaxies within which they reside.

The HerMES project is providing a view of the distant Universe at wavelengths which can only be observed from space. Because the SPIRE camera on board Herschel “sees” images in three sub-millimetre wavelength bands, or colours, which have hardly been used in astronomy until now, it shows a different aspect of galaxies, and is able to view cool objects previously invisible to astronomers. The appearance of an object in these three colours provides information on its temperature, distance and luminosity.

One set of the data being released focusses on a massive cluster of galaxies called Abell 2218. At a distance of over 2 billion light years from Earth, the huge mass of the cluster warps the surrounding space, bending and magnifying light from background galaxies in a manner similar to light being magnified by a normal glass lens. Abell 2218 is famous for being one of the best known examples of this “gravitational lensing”. The effect, first predicted by Einstein in the early 20th century, means that the background galaxies are magnified, allowing a much clearer view of objects as they were over 11 billion years ago – less than 3 billion years after the Big Bang. Without the gravitational lensing these galaxies would be much fainter, and confused by the presence of the foreground galaxies, but this chance alignment provides the opportunity to explore a tiny part of the early Universe in much more detail. The Herschel observations of these distant galaxies tell astronomers how fast they were forming stars at these early times, and help to build up a picture of how galaxies have evolved over the course of billions of years.

The region of sky around the massive galaxy cluster Abell 2218, as seen by Herschel and Hubble. On the left, the images at the three SPIRE wavelength bands are shown, while the centre image is a false-colour composite. The centre of the galaxy cluster is shown as a white cross-hair, while the large yellow blob just below it is a much more distant galaxy. The light from this distant galaxy is being bent and magnified by the immense mass of the Abell 2218 cluster, allowing astronomers to see it in more detail than would otherwise be possible without this chance alignment. It is seen as it was around 2.6 billion years after the Big Bang, providing a glimpse into the Universe’s history. The other structures in the image are largely due to much closer, fainter galaxies which are observed by optical observatories such as the Hubble Space Telescope, as shown on the right. The public release of the Herschel data is allowing astronomers to better determine the formation and evolution of galaxies from soon after the Big Bang right up to today. Click on the image, or here, for more download options. Image credit: ESA/SPIRE and HerMES Consortia (left); ESA/NASA/STScI (right).

The image above shows the Abell 2218 cluster as seen by the SPIRE instrument on Herschel, in relation to an iconic image from the Hubble Space Telescope. The three wavelength bands are first shown as individual red, green and blue images, and then combined into a colour image. The centre of the cluster is marked as a white cross-hair, and the bright yellow object just below is the lensed galaxy. Most of the other galaxies shown are much bluer, and are in the foreground cluster. The properties of the cluster are also of great interest to other astronomers, such as those using the Hubble Space Telescope. Observing at many wavelengths not only helps work out the precise effect of the lensing, but also shows the nature and behaviour of galaxies within large clusters.

Dr. Michael Zemcov of California Institute of Technology says "Images like this show that SPIRE has opened up the possibility of observing at sub-mm wavelengths in a way which was just not possible before; this kind of clarity is unprecedented at these wavelengths. Now that these data are available to the entire astronomical community, we will really be able to test our understanding of objects like galaxy clusters and, more profoundly, the formation of structure in the Universe from soon after the Big Bang right up to the present day."

Richard Ellis, Steele Professor of Astronomy at the California Institute of Technology, who is not a member of the HerMES team but has exploited gravitational lensing in cosmology for over 20 years, added: "It is wonderful to see these first HerMES images which demonstrate the phenomenal power of the Herschel mission. The magnification provided by the rich cluster Abell 2218 and other clusters will provide astronomers worldwide with an unique view of the evolution of early galaxies."

The top of these images shows a nearby galaxy (Messier 82) with high star formation, while on the right is an artist’s impression of an Active Galactic Nucleus (AGN), with a disk of hot dust surrounding a massive black hole. The latest data from the HerMES project is helping to establish the link between the presence of an AGN and the rate of star formation in distant galaxies. Image credits: NASA/ESA/STSci (top); ESA/NASA/AVO/Paolo Padovani (bottom).

Dr. Evanthia Hatziminaoglou, at the European Southern Observatory, has been using the HerMES data to study the connection between galaxies and the super-massive black holes that lie at their centre. These super-massive black holes grow by accreting gas, with some radiating vast quantities of power as quasars or “Active Galactic Nuclei” (AGN). This is the most efficient energy conversion process known. Looking at these objects with Herschel, Dr Hatziminaoglou discovered that their sub-millimetre emission comes almost entirely from star formation and that their properties, in these wavelengths, are indistinguishable from those of non-active galaxies. This result, which will be published next month, confirms independently that super-massive black holes grow in size along with the galaxies in which they reside. Dr Hatziminaoglou said "it is surprising to see that these two highly energetic astrophysical phenomena co-exist in such harmony”.

The HerMES team hope that by releasing catalogues of their galaxies to the whole astronomical community, telescopes around the world will be trained on these kinds of exotic distant beasts to help our understanding of how galaxies and AGN have evolved over the lifetime of the Universe. Professor Ian Smail, an astronomer at Durham University, is not a member of the HerMES team, but uses surveys of galaxies at different wavelengths to study their formation and evolution. Discussing the release of the HerMES catalogues, Prof. Smail said "These first sub-millimetre views of young galaxies in the distant Universe clearly show that huge numbers of new stars are being formed, but cloaked by dust and so missed by optical observatories such as the Hubble Space Telescope. It is already clear that we live in a changing Universe and, thanks to Herschel and SPIRE, few things are changing faster than our perception of it."

Professor Oliver adds “we have made these images and lists of galaxies available to all astronomers sooner than we were obliged to because Herschel is a fantastic mission but has a limited lifetime, and it is vital that it is used for the best science. We hope that other astronomers will want to use Herschel and many other telescopes to study the galaxies we have discovered”.

The Herschel Project Scientist, Göran Pilbratt, said “it is very gratifying that Herschel data are being publicly released. The more people get access to the data, the more productive the mission will be, and the greater its science return. This is a win-win situation for the entire astronomical community.”

Submitted by Chris North

School of Physics and Astronomy
Cardiff University
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Spiral, barred, elliptical and irregular: computers automatically classify galaxy shapes

A picture of the Abell Cluster taken using the Hubble Space Telescope. The picture encapsulates the diversity in galaxy types observed in our Universe. We can see a giant elliptical galaxy at the centre of the cluster, a beautiful spiral in the bottom right-hand corner and many smaller systems displaying a wide range of shapes, sizes and colours. Credit: NASA/ESA and the Hubble Heritage Team (STScI/AURA).

Scientists at University College London (UCL) and the University of Cambridge have developed machine-learning codes modelled on the human brain that can be used to classify galaxies accurately and efficiently. Remarkably, the new method is so reliable that it agrees with human classifications more than 90% of the time. The research will appear in a paper in the journal Monthly Notices of the Royal Astronomical Society.

There are billions of galaxies in the Universe, containing anything between ten million and a trillion stars. They display a wide range of shapes, from elliptical and spiral to much more irregular systems. Large observational projects – such as the Sloan Digital Sky Survey – are mapping and imaging a vast number of galaxies. As part of the process of using these data to better understand their origin and evolution, the first step is to classify the types of galaxies within these large samples. The 250,000 members of the public participating in the Galaxy Zoo project recently classified 60 million such galaxies by eye.

Now, a team of astronomers has used Galaxy Zoo classifications to train a computer algorithm known as an artificial neural network to recognize the different galaxy types. The artificial neural network is designed to simulate a biological neural network like those found in living things. It derives complex relationships between inputs such as the shapes, sizes and colours of astrophysical objects and outputs such as their type, mimicking the analysis carried out by the human brain. This method managed to reproduce over 90% of the human classifications of galaxies.

“We were astonished that a computer could do so well” says Dr Manda Banerji from the Institute of Astronomy at the University of Cambridge who led the research, which formed part of her PhD thesis at UCL. “This kind of analysis is essential as we are now entering a new age of astronomical surveys. Next generation telescopes now under construction will image hundreds of millions and even billions of galaxies over the coming decade. The numbers are overwhelming and every image cannot viably be studied by the human eye.”

A large-scale sky survey in which the UK is playing a leading role is the Dark Energy Survey (DES) due to commence in 2011, which is expected to image 300 million galaxies over 5 years. Another survey called the VISTA Hemisphere Survey being led by astronomers at the University of Cambridge, has just started taking data and will image galaxies over the entire southern hemisphere.

Professor Ofer Lahav, head of Astrophysics at UCL and chair of the international DES Science Committee, who supervised Banerji’s thesis, commented: “While human eyes are very efficient in recognizing patterns, clever computational techniques that can reproduce this behaviour are essential as we begin to push the boundaries of our observable Universe and detect more distant galaxies. This study is an important step in that direction.”

Contacts

Dr Manda Banerji
Institute of Astronomy
University of Cambridge
Tel: +44 (0)1223 765845
Mob: +44 (0)779 294 1499
Email: mbanerji@ast.cam.ac.uk
Web: http://www.ast.cam.ac.uk/~mbanerji/

Professor Ofer Lahav
Perren Chair of Astronomy and Head of Astrophysics
University College London
Tel: +44 (0)20 7679 3473
Email: lahav@star.ucl.ac.uk

Dr Robert Massey
Deputy Executive Secretary
(Public Affairs, Policy, Education and Outreach)
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 / 4582 x. 214
Mob: +44 (0)794 124 8035
Email: rm@ras.org.uk

Further information

The work appears in “Galaxy Zoo: Reproducing Galaxy Morphologies Via Machine Learning”; Banerji M., Lahav O., Lintott C. J., Abdalla F. B., Schawinski K., Bamford S. P., Andreescu D., Murray P., Raddick M. J., Slozar A., Szalay A., Thomas D. and Vandenberg J., Monthly Notices of the Royal Astronomical Society, in press. A pre-print of the paper can be found at http://arxiv.org/abs/0908.2033

Notes for editors

Galaxy Zoo is an online astronomy project which invites members of the public to assist in classifying galaxies. So far more than 250,000 people have assisted in classifying 60 million galaxies. Galaxy Zoo: Hubble, launched in April 2010, invites participants to classify galaxies in the images from the Hubble Space Telescope. http://www.galaxyzoo.org/

The Dark Energy Survey (DES) is a planned galaxy survey that will map 300 million galaxies, with the goal of measuring the properties of Dark Energy. http://www.darkenergysurvey.org/

The VISTA Hemisphere Survey (VHS) is an all-sky near infra-red survey being conducted on the Visible and Infra-Red Telescope for Astronomy (VISTA) in Chile. http://www.vista.ac.uk/

The Royal Astronomical Society

The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

Herschel reveals galaxies in the GOODS fields in a brand new light

The discovery of a previously unresolved population of galaxies in the GOODS fields and the first measurements of properties of galaxies in the almost unexplored far-infrared domain are among the first exciting scientific results achieved by Herschel's PACS and SPIRE instruments. These findings confirm the extraordinary capabilities of ESA's new infrared space observatory to investigate the formation and evolution of galaxies.

These are some of the many discoveries presented this week at the Herschel First Results Symposium, ESLAB 2010, held at the European Space Research and Technology Centre, Noordwijk, The Netherlands.

Understanding the details of how galaxies formed and evolved throughout cosmic history is one of the main goals of current astrophysical research. ESA's Herschel space observatory has begun to address this issue by joining in GOODS - the Great Observatories Origins Deep Survey - an ambitious project conceived to shed new light on this open topic.

Two carefully selected regions of the northern and southern sky, centred on the Hubble Deep Field North and the Chandra Deep Field South, have been the target of deep surveys conducted during the past decade over an extremely broad wavelength range, by means of ESA's and NASA's space observatories and the foremost ground-based telescopes. The GOODS fields, each measuring 10 by 16 arc minutes, are ideal for studying galaxies out to very high redshifts, as they do not contain any bright star and are not contaminated by strong emission coming from the Milky Way.

"Although both GOODS fields have been the object of extensive observations in the past, they have not yet been explored in the far-infrared region of the electromagnetic spectrum," explains Göran Pilbratt, Herschel Project Scientist. "Exploiting Herschel's powerful infrared eye and its broad wavelength coverage, we are now in the process of revealing some of the secrets that have been concealed until now."

Depicts: GOODS-South field

Copyright: ESA/PACS Consortium/PEP Key Programme Consortium

Depicts: PACS composite image of the GOODS-North field

Copyright: ESA/PACS Consortium/PEP Key Programme Consortium

With both the wavelength coverage and the technical characteristics required to resolve this 'cosmic fog' into individual galaxies, Herschel's PACS has isolated the sources of about a half of the CIB in the GOODS fields. "Thanks to the wealth of complementary data available for these fields, we have also studied how many of these galaxies are to be found at various epochs in cosmic history," adds Stefano Berta, who led this study. In fact, most of these galaxies are located at relatively low redshifts, their light having travelled less than 8000 million years before reaching us.

GOODS-N as viewed by SPIRE.

Credit: ESA/SPIRE Consortium/ HerMES Key Programme Consortium

"We know that the energy we receive from galaxies directly is roughly as much as the energy we receive from them after it has been reprocessed by dust," says Seb Oliver from the University of Sussex and leader of the HerMES Key Programme which probes galaxy evolution. "Thanks to SPIRE and PACS, we can finally explore how the population of obscured galaxies has evolved over cosmic time."

The true power of Herschel is unleashed when the images from both instruments are studied together. As a result of this synergy, observations of galaxies made by SPIRE on the GOODS-North field complement the studies on the CIB performed with PACS data. "A significant fraction of galaxies contributing to the CIB has also been resolved by SPIRE," comments Oliver. "This population of galaxies is dominated by sources at z~1, demonstrating that most of the infrared background radiation is emitted at low redshifts," adds Steve Eales from Cardiff University.

By sampling galaxies at the peak of their far-infrared emission, Herschel allows also a better understanding of the star-forming processes taking place within them. "The properties of galaxies in these new PACS and SPIRE images appear surprisingly uniform over the last 10 billion years of cosmic history, even for those galaxies harbouring an active nucleus," says David Elbaz from Laboratoire AIM-Paris-Saclay. This finding suggests that the history of star formation in the Universe is governed by simple, universal mechanisms. "This is only a first step, since a new window on the GOODS fields has just been opened with the GOODS-Herschel Open Time Key Programme. This will push Herschel to its ultimate limits in terms of depth," adds Elbaz.

And it is clear that much more is in store when placing Herschel data in the broader context of the wider electromagnetic spectrum. Some interesting results have already arisen when comparing Herschel data with radio observations of the GOODS-North field performed by the Very Large Array. "We have revealed tantalising signs of an evolution of the famous (and surprisingly strong) correlation between infrared emission and radio emission," notes Rob Ivison from UK Astronomy Technology Centre at the Royal Observatory in Edinburgh.

Notes to Editors

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia, with important participation from NASA.

PACS is an imaging photometer and integral field line spectrometer covering wavelengths between 57 and 210 µm. PACS was built by a consortium of institutes and university departments from across Europe, and is led by Albrecht Poglitsch of the Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany. Consortium members are: Austria: UVIE; Belgium: IMEC, KUL, CSL; France: CEA, OAMP; Germany: MPE, MPIA; Italy: IFSI, OAP/OAT, OAA/CAISMI, LENS, SISSA; Spain: IAC.

The SPIRE instrument comprises an imaging photometer (camera) and an imaging spectrometer. The camera operates in three wavelength bands centred on 250, 350 and 500 μm, and so can make images of the sky simultaneously in three submillimetre "colours". The spectrometer covers the range 200 – 670 μm, allowing the spectral features of atoms and molecules to be measured. SPIRE has been built by a consortium of 18 institutes in eight countries (UK, France, Italy, Spain, Sweden, USA, and China), and is led by Prof. Matt Griffin of Cardiff University. The instrument was assembled at the STFC's Rutherford Appleton Laboratory in the UK.

The PACS data on the GOODS fields have been obtained within the PACS Evolutionary Probe (PEP) collaboration, a Herschel Guaranteed Time Key Programme extragalactic survey, led by Dieter Lutz (Max Planck Institute for extraterrestrial Physics). PEP aims at studying galaxies up to redshift z~3 over a large total area in the sky, including the COSMOS field, the Lockman Hole and fields centred on lensing galaxy clusters. PEP is coordinated with SPIRE observations of the same fields in the Herschel Multi-tiered Extragalactic Survey (HerMES), another Guaranteed Time Key Programme probing galaxy evolution at high redshift. HerMES is led by Seb Oliver (University of Sussex).

Related publications

Berta, S., et al., "Dissecting the Cosmic Infra-Red Background with Herschel/PEP", 2010

Oliver, S.J., et al., "HerMES: SPIRE galaxy number counts at 250, 350 and 500 µm", 2010

Eales, S., et al."First results from HerMES on the evolution of the submillimetre luminosity function", 2010

Elbaz, D., et al., "Herschel unveils a puzzling uniformity of distant dusty galaxies", 2010

Ivison, R.J., et al., "The far-infrared/radio correlation as probed by Herschel", 2010

These papers will appear in a special issue of the journal Astronomy & Astrophysics dedicated to Herschel's first results.

Contacts

Göran Pilbratt, Herschel Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate, ESA, The Netherlands
Email: gpilbrattr@ssd.esa.int
Phone: +31-71-565-3621

Dieter Lutz
Max Planck Institute for extraterrestrial Physics, Germany
Phone: +49 89 300003614
Email: lutz@mpe.mpg.de

Stefano Berta
Max Planck Institute for extraterrestrial Physics, Germany
Phone: +49-89-300003616
Email: berta@mpe.mpg.de

Seb Oliver

University of Sussex, United Kingdom

Phone: +44-1273-678852; mobile number: +44-7971-019161

Email: Oliver@sussex.ac.uk

Steve Eales
Cardiff University, United Kingdom
Phone: +44-29-208-76168
Email: Steve Eales@astro.cf.ac.uk

David Elbaz
Laboratoire AIM-Paris-Saclay, France
Phone: + 33-1-69085439
Email: delbaz@cea.fr

Rob Ivison
UK Astronomy Technology Centre at the Royal Observatory Edinburgh, part of the Science and Technology Facilities Council, United Kingdom
Phone: +44-131-668-8361
Email: rji@roe.ac.uk

Explained: Why many surveys of distant galaxies miss 90% of their targets

PR Image eso1013a
The GOODS-South field

PR Video eso1013a
The GOODS-South field

Astronomers have long known that in many surveys of the very distant Universe, a large fraction of the total intrinsic light was not being observed. Now, thanks to an extremely deep survey using two of the four giant 8.2-metre telescopes that make up ESO’s Very Large Telescope (VLT) and a unique custom-built filter, astronomers have determined that a large fraction of galaxies whose light took 10 billion years to reach us have gone undiscovered. The survey also helped uncover some of the faintest galaxies ever found at this early stage of the Universe.

Astronomers frequently use the strong, characteristic “fingerprint” of light emitted by hydrogen known as the Lyman-alpha line, to probe the amount of stars formed in the very distant Universe [1]. Yet there have long been suspicions that many distant galaxies go unnoticed in these surveys. A new VLT survey demonstrates for the first time that this is exactly what is happening. Most of the Lyman-alpha light is trapped within the galaxy that emits it, and 90% of galaxies do not show up in Lyman-alpha surveys.

“Astronomers always knew they were missing some fraction of the galaxies in Lyman-alpha surveys,” explains Matthew Hayes, the lead author of the paper, published this week in Nature, “but for the first time we now have a measurement. The number of missed galaxies is substantial.”

To figure out how much of the total luminosity was missed, Hayes and his team used the FORS camera at the VLT and a custom-built narrowband filter [2] to measure this Lyman-alpha light, following the methodology of standard Lyman-alpha surveys. Then, using the new HAWK-I camera, attached to another VLT Unit Telescope, they surveyed the same area of space for light emitted at a different wavelength, also by glowing hydrogen, and known as the H-alpha line. They specifically looked at galaxies whose light has been travelling for 10 billion years (redshift 2.2 [3]), in a well-studied area of the sky, known as the GOODS-South field.

“This is the first time we have observed a patch of the sky so deeply in light coming from hydrogen at these two very specific wavelengths, and this proved crucial,” says team member Göran Östlin. The survey was extremely deep, and uncovered some of the faintest galaxies known at this early epoch in the life of the Universe. The astronomers could thereby conclude that traditional surveys done using Lyman-alpha only see a tiny part of the total light that is produced, since most of the Lyman-alpha photons are destroyed by interaction with the interstellar clouds of gas and dust. This effect is dramatically more significant for Lyman-alpha than for H-alpha light. As a result, many galaxies, a proportion as high as 90%, go unseen by these surveys. “If there are ten galaxies seen, there could be a hundred there,” Hayes says.

Different observational methods, targeting the light emitted at different wavelengths, will always lead to a view of the Universe that is only partially complete. The results of this survey issue a stark warning for cosmologists, as the strong Lyman-alpha signature becomes increasingly relied upon in examining the very first galaxies to form in the history of the Universe. “Now that we know how much light we’ve been missing, we can start to create far more accurate representations of the cosmos, understanding better how quickly stars have formed at different times in the life of the Universe,” says co-author Miguel Mas-Hesse.

The breakthrough was made possible thanks to the unique camera used. HAWK-I, which saw first light in 2007, is a state-of-the-art instrument. “There are only a few other cameras with a wider field of view than HAWK-I, and they are on telescopes less than half the size of the VLT. So only VLT/HAWK-I, really, is capable of efficiently finding galaxies this faint at these distances,” says team member Daniel Schaerer.

Notes

[1] Lyman-alpha light corresponds to light emitted by excited hydrogen (more specifically, when the electron around the nucleus jumps from the first excited level to the fundamental, or ground, level). This light is emitted in the ultraviolet, at 121.6 nm. The Lyman-alpha line is the first in the so-called Lyman series, named after its discoverer, Theodore Lyman.

The Balmer series, named after Johann Balmer, also corresponds to light emitted by excited hydrogen. In this case, the electron falls into the first excited level. The first line in this series is the H-alpha line, emitted at 656.3 nm.

As most hydrogen atoms present in a galaxy are in the ground level, Lyman-alpha light is more efficiently absorbed than H-alpha light, which requires atoms having an electron in the second level. As this is very uncommon in the cold interstellar hydrogen permeating galaxies, the gas is almost perfectly transparent to H-alpha light.

[2] A narrowband filter is an optical filter designed to let pass only a narrow bandwidth of light, centred on a specific wavelength. Traditional narrowband filters include those centred on the lines of the Balmer series, such as H-alpha.

[3] Because the Universe expands, the light of a distant object is redshifted by an amount depending on its distance. This means its light is moved towards longer wavelengths. A redshift of 2.2 — corresponding to galaxies whose light has taken approximately 10 billion years to reach us — means that the light is stretched by a factor 3.2. Thus the Lyman–alpha light is now seen at about 390 nm, near the visible domain, and can be observed with the FORS instrument on ESO’s VLT, while the H-alpha line is moved towards 2.1 microns, in the near-infrared. It can thus be observed with the HAWK-I instrument on the VLT.

More information

This research was presented in a paper to appear in Nature (“Escape of about five per cent of Lyman-a photons from high-redshift star-forming galaxies”, by M. Hayes et al.).

The team is composed of Matthew Hayes, Daniel Schaerer, and Stéphane de Barros (Observatoire Astronomique de l'Université de Genève, Switzerland), Göran Östlin and Jens Melinder (Stockholm University, Sweden), J. Miguel Mas-Hesse (CSIC-INTA, Madrid, Spain), Claus Leitherer (Space Telescope Science Institute, Baltimore, USA), Hakim Atek and Daniel Kunth (Institut d'Astrophysique de Paris, France), and Anne Verhamme (Oxford Astrophysics, U.K.).

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 14 countries: Austria, Belgium, 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 Paper

Contacts

Matt Hayes
Observatory of Geneva, Switzerland
Tel: +41 22 379 24 32
Cell: +41 76 243 13 55
Email: matthew.hayes@unige.ch

Miguel Mas-Hesse
Centro de Astrobiologia (CSIC-INTA), Spain
Tel: +34 91 813 1196/1161
Cell: +34 615145651
Email: mm@cab.inta-csic.es

Göran Östlin
Department of Astronomy
Stockholm University, Sweden
Tel: +46 8 55 37 85 13
Email: ostlin@astro.su.se

Henri Boffin
VLT Press Officer
ESO, Garching, Germany
Tel: +49 89 3200 6222
Cell: +49 174 515 43 24
Email: hboffin@eso.org

Underweight or Blinded by Youth? Finding the True Mass of Galaxy Mergers

Fig. 1: Optical (left) and near-infrared (right) comparison between mass (M) and mass-to-light ratio (M/L). The vector shows the evolution of M/L over time. LIRGs (open circles) appear very different in both panels, while non-LIRGs and ellipticals remain the same.

Fig. 2: For luminous infrared galaxy (LIRG) mergers (left), velocity dispersion measured with CO (CO σ0) is significantly lower than that measured with the Calcium II Triplet (CaT σ0). For non-LIRG mergers and normal elliptical galaxies (middle and right), there is no meaningful difference between the two techniques.

Fig. 3: Astronomers have different perspectives on the centers of galaxies at optical (left) and near-infrared (right) wavelengths. Dust prevents optical measurement of the rotating disk of stars that is located at the galaxy's center. Although the dust is still present, it does not obscure near-infrared views

Galaxies are the building blocks of the universe, so accounting for their formation is an essential problem in astronomy. Most galaxies are either spiral or elliptical, with the latter tending to be larger and more massive. One suggestion that is grounded in fundamental measurements of the universe as a whole is that merging spiral galaxies form elliptical galaxies. A way to test the predictions of this merger hypothesis is to observe examples of galaxy merging in process. Barry Rothberg and Jacqueline Fischer of the Naval Research Laboratory (US) have done that, drawing important conclusions about the objects they observed and the techniques astronomers use to measure them.

One critical property of a galaxy is its mass. The motion of stars is sensitive to the gravitational effect of the mass, so measuring the stellar motion can yield a galaxy's mass. Observations of characteristic features in the spectra of stars are sensitive to this motion. Specifically, measurement of CO at near-infrared wavelengths is a common diagnostic, especially in dusty luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs). A surprising aspect of past near-IR studies of merging galaxies is that the resulting elliptical galaxies would have relatively low mass, while previous optical studies by Rothberg using the calcium II triplet at 0.85µm show that they would have large masses. Is there a fundamental problem with using the CO measurements for all galaxies, or is something strange happening only in the LIRGs and ULIRGs that had been studied? As Rothberg says, "Either possibility would have a significant impact on galaxy dynamical studies. The only instrument that could answer this question definitively was GNIRS (Gemini Near-Infrared Spectrograph), because of the unique combination of spectral and spatial resolution and the need for an 8-meter mirror to gather enough light."

In the new work, Rothberg and Fischer find that IR-luminous mergers appear younger and less massive in the near-IR but indistinguishable from old, massive ellipticals at optical wavelengths (Figure 1). The fundamental measurement of these two diagnostics (the velocity dispersion) is different in the LIRGs, where CO shows smaller velocity dispersion and therefore indicates smaller mass. Normal elliptical galaxies and merger remnants that are not IR-luminous, however, do not show any significant difference between the optical and near-IR measurements (Figure 2). GNIRS provided the critical observations to show that CO measurements cannot be used to determine the mass of LIRGs and ULIRGs.

Why are these IR-luminous merging galaxies different, and what do their CO measurements mean? The strong infrared emission from these systems arises in the dusty environments of recent bursts of star formation. The CO measurements are sensitive to these younger stars, and they even show a rotating disk of young stars in rotation curves. Thus, in these luminous IR galaxies, the CO does not probe the total mass of the merger remnant but traces the rotating young central stellar disk instead. Optical light cannot penetrate the dusty centers of these systems, so these central stellar disks do not affect the calcium II triplet diagnostic, and it measures the mass of the entire merger (Figure 3). After the merging systems have settled to become regular elliptical galaxies, however, they no longer exhibit the confusion of recent star formation and obscuring dust, so optical and infrared measurements are consistent with each other.

The complete results (published in the Astrophysical Journal 2010, Vol. 712, page 318) use data from the University of Hawaii 2.2 meter, Keck, and Hubble Space telescopes in addition to Gemini. GNIRS is currently being repaired, and it will be deployed on the Gemini North telescope later this year.

Young galaxies gorge on gas

Fig. 1: The Plateau de Bure millimetre interferometer in the southern French Alps.
Copyright: IRAM

Fig. 2: Spatially resolved optical and millimetre images of a typical massive galaxy at redshift z=1.1 (5.5 billion years after the Big Bang). The left image was taken with the Hubble Space Telescope in the V- and I-optical bands, as part of the AEGIS survey of distant galaxies. The right image is an overlay of the CO 3-2 emission observed with the PdBI (red/yellow colours) superposed on the I-image (grey). For the first time these observations clearly show that the molecular line emission and the optical light from massive stars trace a massive, rotating disk of diameter ~60,000 light years. This disk is similar in size and structure as seen in z~0 disk galaxies, such as the Milky Way. However, the mass of cold gas is in this disk is about an order of magnitude larger than in typical z~0 disk galaxies. This explains why high-z galaxies can form continuously at about ten times the rate of typical z~0 galaxies. Copyright: MPE/IRAM

Scientists find explanation for higher star formation rate in young galaxies

Stars form from giant gas clouds in galaxies - the star formation rate however has changed over cosmic timescales. In the young universe many more stars were born. Scientists from the Max Planck Institute for extraterrestrial Physics, together with an international team of astronomers have found a plausible explanation: a few billion years after the Big Bang, normal star forming galaxies contained five to ten times more cold gas than today, providing more "food" to fuel the star formation process.

"We have been able, for the first time, to detect and image the cold molecular gas in normal star forming galaxies, which are representative of the typical massive galaxy populations shortly after the Big Bang" said Linda Tacconi from the Max Planck Institute for extraterrestrial Physics, who is the lead author of a paper in this week's issue of Nature.

The challenging observations yield the first glimpse how galaxies, or more precisely the cold gas in these galaxies, looked a mere 3 to 5 billion years after the Big Bang (equivalent to a cosmological redshift z~2 to z~1). At this epoch, galaxies seem to have formed stars more or less continuously with at least ten times the rate seen in similar mass systems in the local Universe.

The fundamental question is whether these large star formation rates were caused by larger reservoirs of cold molecular gas (which represents the 'food' for newly formed stars), or whether star formation in the young Universe was much more efficient than it is today.

Over the past decade astronomers have established a global framework of how galaxies formed and evolved when the Universe was only a few billion years old. Gas cooled and collected in concentrations of the mysterious 'dark' matter (so called dark matter halos). Over cosmological timescales, gas accreting from these halos onto the proto-galaxies, and collisions and mergers of galaxies subsequently led to the hierarchical build-up of galaxy mass.

Detailed observations of the cold gas and its distribution and dynamics hold a key role in disentangling the complex mechanisms responsible for turning the first proto-galaxies into modern galaxies, such as the Milky-Way.

A major study of distant, luminous star forming galaxies at the Plateau de Bure millimetre interferometer (Figure 1) has now resulted in a break-through by having a direct look at the star formation "food". The study took advantage of major recent advances in the sensitivity of the radiometers at the observatory to make the first systematic survey of cold gas properties (traced by a rotational line of the carbon monoxide molecule) of normal massive galaxies when the Universe was 40% (z=1.2) and 24% (z=2.3) of its current age. Previous observations were largely restricted to rare, very luminous objects, including galaxy mergers and quasars. The new study instead traces massive star forming galaxies representative of the 'normal', average galaxy population in this mass and redshift range.

"When we started the programme about a year ago", says Dr. Tacconi, "we could not be sure that we would even detect anything. But the observations were successful beyond our most optimistic hopes. We have been able to demonstrate that massive normal galaxies at z~1.2 and z~2.3 had five to ten times more gas than what we see in the local Universe. Given that these galaxies were forming gas at a high rate over long periods of time, this means that gas must have been continuously replenished by accretion from the dark matter halos, in excellent agreement with recent theoretical work."

Another important result of these observations is the first spatially resolved images of the cold gas distribution and motions in several of the galaxies (Figure 2). "This survey has opened the door for an entirely new avenue of studying the evolution of galaxies," says Pierre Cox, the director of IRAM. "This is really exciting and there is much more to come."

"These fascinating findings provide us with important clues and constraints for next-generation theoretical models that we will use to study the early phases of galaxy development in more detail," says Andreas Burkert, specialist for star formation and the evolution of galaxies at the Excellence Cluster Universe. "Eventually these results will help to understand the origin and the development of our Milky Way."

Notes:

[1] The scientists involved in the study are:
N. Bouché, N.M. Förster Schreiber, R. Genzel, J.Gracia-Carpio, D. Lutz, L.J. Tacconi (all Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany), P.Cox, R.Neri (IRAM, France), M.C.Cooper, B.Weiner (University of Arizona, USA), K.Shapiro, J.Comerford, M.Davis (University of California, Berkeley, USA), A.Bolatto (University of Maryland, USA), F.Bournaud (CEA, Gif-sur-Yvette, France), A.Burkert, T.Naab (University of Munich (LMU) and Excellence Cluster, Munich, Germany), F.Combes (Observatoire de Paris, France), S.Garcia-Burillo (Madrid Observatory (OAN), Madrid, Spain), A.Omont (Instiute d'Astrophysique, Paris, France), A.E. Shapley (University of California, Los Angeles, USA), A. Sternberg (Tel Aviv University, Israel). R.Genzel is also associated with the Physics Department at the University of California, Berkeley (USA).

[2] The Plateau de Bure millimetre interferometer of the Institute for Radio Astronomy in the Millimetre Range (IRAM) is located at 2600m in the southern French Alps near Gap. The PdBI is currently the most powerful millimetre interferometer in the world, and the only one capable of detecting the faint line emission of CO molecules from very distant galaxies, which are the best tracer for cold gas (mainly molecular hydrogen). The interferometer consists of 6 telescopes of 15m diameter, each equipped with superbly sensitive heterodyne radiometers to detect mm-radiation. IRAM is funded by a partnership of INSU/CNRS (France), MPG (Germany) and IGN (Spain).

For more information on IRAM and the PdBI : external link http://www.iram-institute.org/

Original paper:

L.J.Tacconi et al.
High molecular gas fractions in normal massive star forming galaxies in the young Universe
Nature 463, 781-784 (11 February 2010)

Press release:

MPG press release on February 10, 2010 (in German)

Contact:

Dr. Hannelore Hämmerle
Press Officer
Max Planck Institute for Astrophysics
and Max Planck Institute for extraterrestrial Physics
Phone: +49 89 30000-3980
E-Mail: hannelore.haemmerle@mpe.mpg.de

Reinhard Genzel internal link Prof. Dr. Reinhard Genzel
Infrared/Submillimeter Astronomy Group
Max Planck Institute for extraterrestrial Physics
Phone: +49 89 30000-3280
E-Mail: genzel@mpe.mpg.de

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Discovery of New Stellar Streams in the Andromeda Galaxy Shows Galaxy Formation Through Mergers

Figure 1：Illustration of a galactic structure in the edge-on view. A stellar halo has a huge size with a diameter of over 500,000 light years and contains old halo stars and globular clusters.

Figure 2：Traditional view of the Andromeda galaxies, showing only its bright bulge and inner disk and extending out to a projected distance of only about 65,000 light years from the galaxy's center. Image credit: National Astronomical Observatory of Japan.

Figure 3：False-color map of the density of red giant stars in Andromeda, constructed from Subaru/Suprime-Cam images. The stellar density enhancements in Streams E, F, and SW are indicated. The map extends out to a projected distance of 300,000 light years from Andromeda's center. Image credit for star count map: Mikito Tanaka (Tohoku University).

Figure 4：Distribution of line-of-sight velocities of stars in the Stream SW field. The filled portion of the histogram corresponds to Andromeda red giant stars while the open portion corresponds to foreground Milky Way stars. The concentration of red giant stars (at a velocity of -370 kilometers per second) is characteristic of tidal streams. Image credit: Puragra Guhathakurta (University of California, Santa Cruz).+

A team of astronomers from Tohoku University, University of Tokyo, NAOJ, University of California Santa Cruz, and other universities (Note 1) have discovered new stellar streams in a vast region surrounding the disk of Andromeda, in its so-called stellar halo. These stellar or tidal streams (Note 2), which are localized in space and move as a coherent group through the parent galaxy, intensify the density of stars and are remnants of past mergers of relatively small (i.e., dwarf) galaxies. The data from the team's observations using both Subaru's Suprime-Cam for photometry and Keck II's Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS) for spectroscopy provided detailed spatial and velocity distributions of the stellar streams and led to this discovery.

Stars spread over the vast reaches of a halo in a big galaxy like the Milky Way or Andromeda Galaxy (Figure 1) are characterized by old age, few elements other than helium and hydrogen (i.e., low metallicities), and high velocities. The exceptional nature of these halo stars, when compared to stars in a galaxy's disk, reflects the early dynamics and chemical evolution of the galaxy when its appearance differed significantly from what we see today. Consequently, the halo provides important insights into the processes involved in the formation and evolution of a massive galaxy. According to the current theory of galaxy formation, we expect a halo to preserve evidence of past galaxy mergers and/or tidal dissolution in the course of halo formation.

Since the merging and dissolution of a dwarf galaxy typically last for a couple of billion years, these events are occasionally seen in a large galaxy. Given the assumption that past merging events are recorded as stellar streams, identification of these stellar substructures in a halo plays a key role in studying the past history of galaxies. The Andromeda Galaxy is an excellent test case for this purpose: it is the nearest, large spiral galaxy similar to our own Milky Way Galaxy (Figure 2) and is close enough for individual stars to be studied in great detail.

Motivated by the scientific significance of examining Andromeda's halo, an international research team led by Mikito Tanaka (Tohoku University) carried out photometric observations of Andromeda's halo fields with V and I bands of Suprime-Cam, a wide field imager mounted on the Subaru Telescope. Rather than spending an enormous number of observation nights mapping its entire halo, the team looked at specific portions of Andromeda's minor axis fields, including the hitherto uncharted north side as well as some fields at the major axis. This survey led to the discovery of two stellar streams to the northwest (Streams E and F: Figure 3) at projected distances of 200,000 and 300,000 light years from Andromeda's center. The study also confirmed a few previously known streams, including the little-studied diffuse stream to the southwest (Stream SW: Figure 3), which lies at a projected distance of 200,000 to 300,000 light years from Andromeda's center.

Another scientific team led by Puragra Guhathakurta (University of California, Santa Cruz) followed up the photometric observations with a spectroscopic survey of several hundred red giant stars in Streams E, F, and SW, using Keck II's 10-meter telescope fitted with DEIMOS. Red giant stars are large, bright stars with low or intermediate mass that are in a late phase of stellar evolution. Because the spectrograph spreads out the light from each star into a spectrum, it allows astronomers to measure the star's velocity and thus distinguish Andromeda red giant stars from foreground stars in the Milky Way. The spectral data confirmed the presence of coherent groups of Andromeda red giant stars moving with a common velocity (Figure 4).

The features of these newly discovered stellar streams in Andromeda are evidence of past galaxy mergers associated with the formation of a stellar halo. The next research step will be to measure in detail the chemical properties of Andromeda's giant red stars within their stellar streams. Mikito Tanaka anticipated the significance of future research by saying, "Further observational surveys of an entire halo region in Andromeda will provide very useful information on galaxy formation, including how many and how massive individual dwarf galaxies as building blocks are and how star formation and chemical evolution proceeded in each dwarf galaxy."

The photometric survey of Andromeda with Subaru's Suprime-Cam was published in a recent ApJ article (Note 3). Findings from the spectroscopic survey with Keck/DEIMOS were presented at the 215th meeting of the American Astronomical Society in Washington, D.C. (Note 4).

Note 1: Mikito Tanaka (Tohoku University, University of Tokyo), Masashi Chiba (Tohoku University), Yutaka Komiyama (NAOJ), Masanori Iye (NAOJ), Puragra Guhathakurta (University of California, Santa Cruz), Jason S. Kalirai (Space Telescope Science Institute), and other collaborators at the University of Virginia, UC Irvine, University of Massachusetts, Yale University, University of Washington, Columbia University, and California Institute of Technology.

Note 2: Stellar streams represent enhancements in the density of stars, localized in space and moving as a coherent group through the parent galaxy. Because tidal forces play a role in their creation, they are also referred to as tidal streams. These substructures in stellar distribution are remnants of past merging events of dwarf galaxies when they fall into a big galaxy like the Milky Way and Andromeda.

Note 3: "Structure and Population of the Andromeda Stellar Halo from a Subaru/Suprime-Cam Survey" by Mikito Tanaka, Masashi Chiba, Yutaka Komiyama, Puragra Guhathakurta, Jason S. Kalirai, Masanori Iye, 2010, ApJ, 708, 1168-1203

Note 4: "The SPLASH Survey: Spectroscopy of Newly Discovered Tidal Streams in the Outer Halo of the Andromeda Galaxy" by Puragra Guhathakurta, R. Beaton, J. Bullock, M. Chiba, M. Fardal, M. Geha, K. Gilbert, K. Howley, M. Iye, K. Johnston, J. Kalirai, E. Kirby, Y. Komiyama, S. Majewski, R. Patterson, M. Tanaka, E. Tollerud, SPLASH collaboration, 2010, AAS Meeting #215, #354.01

Hubble's deepest view of Universe unveils never-before-seen galaxies

Images: Image 1 - Image 2 - Image 3 - Image 4 - Print Layout

Videos

The new Wide Field Camera 3 aboard the NASA/ESA Hubble Space Telescope has taken the deepest image yet of the Universe in near-infrared light. The faintest and reddest objects in the image are likely the oldest galaxies ever identified, having formed between only 600–900 million years after the Big Bang.

In 2004, Hubble created the Hubble Ultra Deep Field (HUDF), the deepest visible-light image of the Universe, and now, with its brand-new camera, Hubble is seeing even farther. This image was taken in the same region as the visible HUDF, but is taken at longer wavelengths. Hubble’s newly installed Wide Field Camera 3 (WFC3) collects light from near-infrared wavelengths and therefore looks even farther back towards the Big Bang, because the light from hot young stars in these very distant galaxies is stretched out of the ultraviolet and visible regions of the spectrum into near-infrared wavelengths by the expansion of the Universe. This new deep view also provides insights into how galaxies grew in their formative years early in the Universe's history.

A boon to astronomers worldwide, the new WFC3 data — taken by the HUDF09 team — have set a multitude of teams to work, furiously searching for the most distant galaxies yet discovered. In just three months, twelve scientific papers on these new data have been submitted.

This image was taken by the HUDF09 team [1], which has made it available for research by astronomers worldwide. The photo was taken with the new WFC3/infrared camera on Hubble in late August 2009, during a total of four days of pointing for 173 000 seconds of total exposure time. Infrared light is invisible to the human eye and therefore does not have colours that can be perceived. The representation is "natural" in that shorter infrared wavelengths are represented as blue and the longer wavelengths as red. The faintest objects are about one billion times fainter than the dimmest visible objects seen with the naked eye.

These Hubble observations are blazing a trail for Hubble’s successor, the NASA/ESA James Webb Space Telescope (JWST), which will look even farther into the Universe than Hubble, at infrared wavelengths. The launch of JWST is planned for 2014.

Notes for editors:

[1] The HUDF09 team members are Garth Illingworth (University of California Observatories/Lick Observatory and the University of California, Santa Cruz), Rychard Bouwens (University of California Observatories/Lick Observatory and Leiden University), Pascal Oesch and Marcella Carollo (Swiss Federal Institute of Technology, Zurich (ETH)), Marijn Franx (Leiden University), Ivo Labbe (Carnegie Institute of Washington), Daniel Magee (University of California, Santa Cruz), Massimo Stiavelli (Space Telescope Science Institute), Michele Trenti (University of Colorado, Boulder), and Pieter van Dokkum (Yale University).Image credit: NASA, ESA, G. Illingworth (UCO/Lick Observatory and the University of California, Santa Cruz), R. Bouwens (UCO/Lick Observatory and Leiden University) and the HUDF09 Team

Links:

NASA release
Oxford release
Wilkins et al. science paper
McLure et al. science paper
Bunker et al. science paper

Contacts:

Garth Illingworth
University of California Observatories/Lick Observatory and University of California, Santa Cruz
Tel: +1-831-459-2843
E-mail: gdi@ucolick.org

Colleen Sharkey
Hubble/ESA, Garching, Germany
Tel: +49-89-3200-6306
Cell: +49-151-1537-3591
E-mail: csharkey@eso.org

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
Tel: +1-410-338-4514
E-mail: villard@stsci.edu

Herschel Takes a Peek at the Ingredients of the Galaxies

The European Space Agency has today (25th Nov) released spectacular new observations from the Herschel Space Observatory, including the UK-led SPIRE instrument. Spectrometers on board all three Hershel instruments have been used to analyse the light from objects inside our galaxy and from other galaxies, producing some of the best measurements yet of atoms and molecules involved in the birth and death of stars.

The SPIRE Fourier Transform Spectrometer (FTS), which covers the whole submillimetre wavelength range between 194 and 672 microns, will be invaluable to astronomers in determining the composition, temperature, density and mass of interstellar material in nearby galaxies and in star-forming clouds in our own galaxy.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), which provides the UK funding for Herschel, said “Herschel has once again returned some spectacular indications of what is to come. This wealth of new data exists because of the dedication and skill of the scientists working on this project and will vastly expand our knowledge of the life cycle of stars.”

Professor Matt Griffin of Cardiff University, who is the SPIRE Principal Investigator, said: “Some trial observations have been made during initial testing of the spectrometer, and it is clear that the data are of excellent quality, and even these initial results are very exciting scientifically, especially our ability to trace the presence of water throughout the Universe. The spectrometer was technically very challenging to build, and the whole team is delighted that it works so well.”

Professor Glenn White, of the Open University and STFC’s Rutherford Appleton Laboratory, and an expert in the field of molecular astronomy for which the SPIRE spectrometer is designed, said: "The exquisite sensitivity and quality of these early data reveal spectacular spectroscopic signatures that show the diversity and complexity of the birth processes common to the formation of star and planets. Herschel is going to help us trace the evolution and life of stars, to map the chemistry in our galactic neighbourhood, and allow us to detect water and complex molecules in distant galaxies."

Professor Mike Barlow of University College London, who will use the SPIRE instrument to study the material ejected into space by stars near the end of their lives, said: “The unprecedented spectral range and the wealth of detail revealed by the SPIRE spectrometer, in a hitherto almost unexplored region of the spectrum, promises to revolutionise our understanding of the formation of molecules and dust particles during the final stages of the lives of stars. These dust particles go on to play a crucial role in the formation of new stars and provide the raw material for the planetesimals and planets that form around them."

Figure 1 shows part of the SPIRE spectrum of VY Canis Majoris (VY CMa), a giant star near the end of its life, which is ejecting huge amounts of gas and dust into interstellar space, including elements such as carbon, oxygen and nitrogen (which form the raw material for future planets, and eventually life). The inset is a SPIRE camera image of VY CMa, in which it appears as a bright point-source near the edge of a large extended cloud. The spectrum is amazingly rich, with prominent features from carbon monoxide (CO) and water (H2O). More than 200 other spectral features have also been identified, many due to water, showing that the star is surrounded by large quantities of hot steam. Observations like these will help to establish a detailed picture of the mass loss from stars and the complex chemistry occurring in their extended envelopes.

Figure 2 is a spectrum of one position on the Orion Bar, part of the Orion nebula in which the gas on the edge of the nebula is partly ionised by intense radiation from nearby hot young stars. The inset shows a near infrared picture from NASA’s Spitzer Space Telescope. The SPIRE spectrum has many features from CO, appearing as the dominating narrow lines, seen here for the first time together in a single spectrum. These mean that the entire spectrum is observed at the same time and calibrated together. The brightness of the spectral features will allow astronomers to estimate the temperature and density of interstellar gas. The spectrum also shows the first detection of an emission feature from the molecular ion methylidynium (CH+), a key building block for larger carbon-bearing molecules. This and similar regions are large, and the SPIRE spectrometer’s will be extremely powerful in characterising how the gas properties vary within such sources.

Figure 3 shows a SPIRE spectrum of Arp 220, a galaxy 250 million light years away from Earthwith very active star formation triggered when two large spiral galaxies collided to produce the complex object we see today. Arp 220 is an important template for understanding even more distant galaxies and galaxy formation in the early universe. The spectrum shows many emission features of CO, and H2O features are seen both in emission and absorption. The inset is an optical image of Arp 220 made with the Hubble Space Telescope.

Figure 4 shows the spectrum of Messier 82 (M82), a nearby galaxy (only 12 million light years away) with very active star formation. It is part of an interacting group of galaxies including the large spiral M81. The accompanying image (inset) is a spectacular three-colour composite picture of the two galaxies made with the SPIRE camera, showing material being stripped from M81 by the gravitational interaction with M82. The SPIRE spectrum of M82 shows strong emission lines from CO over the whole wavelength range, as well as emission lines from atomic carbon and ionized nitrogen.

The SPIRE FTS observations were carried out as part of the performance verification of the observatory. The scientific rights of some of these observations are owned by Key Programme consortia: for Arp 220 and M82, the Nearby Galaxies consortium lead by C. Wilson; for VY CMa the MESS consortium led by M. Groenewegen; for the Orion Bar, the Evolution of Interstellar Dust consortium led by A. Abergel.

Notes for editors

Images (hires) : Figure 1 - Figure 2 - Figure 3 - Figure 4

Further details of the new observations by SPIRE, and by the other two Herschel instruments, may be found at the ESA Herschel Science Centre web site .

UK Herschel site

The SPIRE Fourier Transform Spectrometer covers the submillimetre wavelength range (194–672 microns), and provides a complete survey of the source spectrum over that whole wavelength range in a single observation, something that has never been possible with previous submillimetre instruments.

At the same time as measuring the intensities of narrow spectral features from gas atoms and molecules, the SPIRE spectrometer also accurately measures the broadband emission from dust. With its multi-pixel detector arrays, it can also produce spectral images, allowing astronomers to measure the spatial variation in the interstellar material.

Herschel and SPIRE

The European Space Agency’s Herschel satellite carries the largest telescope to be flown in space and is designed to study the Universe at far infrared wavelengths. It will reveal the early stages of star birth and galaxy formation; it will examine the composition and chemistry of comets and planetary atmospheres in the Solar System; and it will examine the star-dust ejected by dying stars into interstellar space which form the raw material for planets like the Earth.

The SPIRE instrument has been built by a consortium of 18 institutes in eight countries (UK, France, Italy, Spain, Sweden, USA, Canada and China), led by Prof. Matt Griffin of Cardiff University. The instrument was assembled at the STFC’s Rutherford Appleton Laboratory in the UK.

UK Participation in Herschel

The UK contribution to Herschel includes leadership of the international consortium that designed and built the SPIRE instrument. The UK SPIRE team is also responsible for the development of software for instrument control and processing of the scientific data, and leads the in-flight testing and operation of SPIRE. The Herschel programme in the UK is funded by the Science and Technology Facilities Council.

SPIRE comprises a three band imaging photometer and an imaging Fourier transform spectrometer and has been designed and built by a consortium of institutes including a number from the UK (Cardiff University; Imperial College, London; University College London’s Mullard Space Science Laboratory; the University of Sussex; and STFC’s Rutherford Appleton Laboratory and UK Astronomy Technology Centre). The UK is also leading the development of software for controlling the instrument from the ground and processing the data to produce scientific results. The SPIRE Operations Centre, responsible for delivering all instrument software to ESA, and for day-to-day instrument monitoring, operation, and calibration, is located at the Rutherford Appleton Laboratory with contributions from the Imperial College and Cardiff groups. The UK SPIRE institutes, together with astronomers in many other UK universities, are also strongly involved in the Herschel scientific programmes which have already been selected for the first 18 months of Herschel observations, and cover a wide range of science topics from our own solar system to the most distant galaxies.

Contacts

Julia Short
Press Officer
Science and Technology Facilities Council
Tel: +44 (0) 1793 44 2012

Mr. Chris North
UK Herschel Outreach Officer
School of Physics and Astronomy
Cardiff University
Tel: +44 (0)29 208 70537 or 76403

Prof. Matt Griffin
Herschel-SPIRE Principal Investigator
School of Physics and Astronomy
Cardiff University
Tel: +44 (0)29 2087 4203

Prof. Glenn White
Dept. of Physics & Astronomy
The Open University
Walton Hall
Milton Keynes MK7 6AA
Tel: +44 (0)1908 652 735

Prof. Mike Barlow
Department of Physics and Astronomy
University College London
Gower Street
London WC1E 6BT
Tel: +44 (0)20 7679 7160

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