WELCOME TO A MENAGERIE OF A MILLION GALAXIES
SUBARU/XMM-NEWTON DEEP SURVEY TEAM RELEASES DATA TO THE PUBLIC
June 1, 2004
Name: Subaru XMM-Newton Deep Field
Resolution JPEG Image (116KB)
- High Resolution JPEG Image (541KB)
A color composite image of the Subaru/XMM-Newton Deep Field. Five Suprime-Cam pointings cover a 1.3° x 1.3° field centered at α = 02h18m, δ = −05° 00′ (2000.0). The images of the Moon and the full SXDS field have the same scale.
At a press conference held on 3 PM (JST), June 1, 2004, in Tokyo Japan, the National Astronomical Observatory of Japan (NAOJ) unveiled visible, X-ray, and radio wavelength images of the Subaru/XMM-Newton Deep Survey, based on data from the Subaru telescope, the European Space Agency's (ESA) XMM-Newton Observatory and the Very Large Array. SXDS provides a comprehensive population census of galaxies from the early Universe to the present. The image release coincides with the public release of SXDS's visible wavelength scientific data from Subaru telescope. By inviting both amateur and professional astronomers to explore this menagerie of over a million galaxies, the SXDS survey team hopes to maximize the scientific output from this remarkable data set. The web site for the Subaru data is: http://www.naoj.org/Science/SubaruProject/SDS/
One of the fundamental goals of modern astronomy is understanding the history of the Universe, and in particular learning about the processes which shape the formation and evolution of galaxies. It is possible to observe these processes unfold by surveying galaxies near and far over a large enough volume of the Universe so that local variations in the physical properties and the distribution of galaxies do not skew the results. The Subaru/XMM-Newton Deep Survey (SXDS) is the first multi-wavelength survey which has sufficient width and depth to accurately characterize the properties of galaxies from the early Universe to the present. Both Subaru and XMM-Newton have devoted a considerable amount of time to the SXDS. The XMM-Newton observations represent the deepest and most sensitive wide area X-ray survey ever carried out by XMM-Newton, totalling over 400 thousand seconds of exposure time. The Subaru telescope has stared at this field for over 200 hours, in four different colors, revealing details which are a hundred million times fainter than what can be seen with the naked eye. The large volume explored by the SXDS reveals over a million galaxies, of all types and sizes, and in a range of environments. The field is in the constellation Cetus, which is visible in the southern evening sky from most northern latitudes in the fall. The survey area is 1.3 square degrees, about seven times the area of the full moon, and 850 times the survey area of the famous Hubble Deep Field. The SXDS also encompasses a broad wavelength range from short wavelength X-rays to long wavelength radio waves. The multi-wavelength data provide a detailed description of the various types of galaxies that populate the Universe, but they can be also be used to estimate distances to all the galaxies - yielding a three dimensional map. Due to the finite speed of light, we see more distant galaxies as they were longer ago, and a 3D map shows us how galaxies have changed with time. The history of galaxies places strong constraints on cosmological models that determine the ultimate fate of our Universe. The SXDS team, an international collaboration of astronomers from the National Astronomical Observatory of Japan (NAOJ), the University of Tokyo, the Institute of Space and Astronautical Science (ISAS), the University of Durham, and Tohoku University working in close collaboration with the XMM-Newton Survey Science Centre (SSC) led by the University of Leicester, are already obtaining a wealth of scientific results which will be the topic of discussion at a science workshop in Kyoto, Japan, from June 3 - 5, 2004. For example, Dr. Tadayuki Kodama and others have been able to show that larger galaxies form earlier and evolve faster than smaller galaxies. A team led by Dr. Yoshihiro Ueda have shown that galaxies with massive black holes in their centers are distributed in a pattern with a characteristic length scale of 100 million light years. The observational data and object catalog from the Subaru telescope that led to these discoveries are now publicly available on the internet to astronomers throughout the world. "By releasing the data beyond our own group, we hope to realize the full scientific potential of the data", says Dr. Kazuhiro Sekiguchi, coordinator of the Japanese SXDS team. "With a large and comprehensive data set like this, there are innumerable research possibilities. We can encourage rigorous science by allowing other researchers to test their observational or theoretical results against ours. Other researchers -- professionals, amateurs, and students -- can look at our data with a new perspective and begin answering questions that we may have overlooked, or don't have the time or human resources to address," says Dr. Sekiguchi. Although the SXDS data are already a treasure trove of information, their scientific value will multiply when observations at wavelengths that complement the existing data are complete. These include ultra-violet (0.1-0.3 microns), near-infrared (1-2.5 microns), mid and far-infrared (3-160 microns) and sub-millimeter (250 to 1000 microns) imaging and optical spectroscopy from a wide range of international facilities. In five years, when the survey is scheduled to conclude, SXDS should place strong constraints on the cosmological models that determine the ultimate fate of the Universe, providing insights into both the past and the future.
| A three color composite
image of the Subaru/Suprime-Cam data
Low Res. (1/32 scale) JPEG Image (370KB)
Mid. Res. (1/16 scale) JPEG Image (1.6MB)
High Res. (1/8 scale) JPEG Image (6.2MB)
| An X-ray spectral color composite
image of the XMM-Newton data
JPEG Image (80KB)
Information of an X-ray representation
| A radio map of the VLA data
GIF Image (1.4MB)
Close-up JPEG Image (155KB)
| A star chart of the location of the
GIF Image (27KB)
| An illustration of the relative positions
of the visible and X-ray data
JPEG Image (50KB)
| An illustration of the multi-wavelength
proposed for SXDS
JPEG Image (260KB)
| Highlights from the Subaru/Suprime-Cam
Composite Image (46KB)
| Snapshots of the galaxy SXDF021823.6-052501
in radio, visible, and X-ray wavelengths
JPEG Image (1.3MB)
Kodama, T. et al. 2004
"Down-Sizing in Galaxy Formation at z~1 in the Subaru/XMM-Newton Deep Survey (SXDS)"
Published in the May 2004 edition of the Monthly Notices of the Royal Astronomical Society MNRAS, 350, 1005
The SXDS Home Page
The European Space Agency's Press Release Site
SXDS Team Member List
Dr. Kazuhiro Sekiguchi
(USA: 1) 808-934-5905
(Japan: 81) 90-4565-4275 (May 31 - June 5)
kaz at subaru.naoj.org
Dr. Masatoshi Imanishi
(Japan: 81) 422-34-3538
imanishi at optik.mtk.nao.ac.jp
- What are the scientific data now available?
- What other observations are being carried
out on the SXDS field?
- What other observations may be proposed?
- Why do you need a deep and wide survey?
- Why do you need to observe at multiple
- What do the different wavelength images
- How do you determine the distances to
- What are some of the scientific results
- Where can I find more information on the various telescopes that may be used to observe the SXDS field?
Optical imaging data from Subaru telescope's prime focus camera Suprime-Cam (http://www.naoj.org/Science/SubaruProject/SDS/). The data consists of B-band (central wavelength 0.4 microns), R-band (0.7 microns), i'-band (0.8 microns) and z'-band (0.9 microns) to a faintness of 28.2 magnitudes in B-band, which is several hundred million times fainter than what can be observed by the naked eye.
X-ray imaging data from the EPIC camera (European Photon Imaging Camera) onboard ESA's XMM-Newton Observatory. The energy range of the X-ray data is 0.5 to 10.0 keV, equivalent to wavelengths of 1/8000 to 1/400 microns.) These are available through the XMM-Newton Science Archive.
A catalog of all the astronomical objects detected in the Subaru/Suprime-Cam data.
Sub-millimeter observations with the Sub-millimeter Common User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT) on Mauna Kea. The SXDS field will be covered as part of the SCUBA HAlf Degree Extragalactic Survey (SHADES). JCMT will be dedicating a substantial fraction of its total observing time over three years to carry out SHADES, the largest ground based sub-millimeter survey ever undertaken to date. The survey began in 2002 and is expected to be completed in 2005.
The Balloon-borne Large Aperture Sub-millimeter Telescope (BLAST) will take sub-millimeter data of wavelengths inaccessible from the Earths surface (250-500 microns).
Near-infrared imaging with Wide Field Infrared Camera (WFCAM) on the United Kingdom Infrared Telescope on Mauna Kea. The SXDS field will be included in the Ultra Deep Survey (UDS) of the United Kingdom Infrared Telescope Infrared Deep sky Survey (UKIDSS) that will obtain deep wide field imaging in the 1 to 2.5 micron range. The UKIDSS survey will begin in 2004, and approximately 300 nights of observing will be dedicated to the UDS survey over 5 years.
Mid to far-infrared observations (3 - 160 microns) with NASA's Spitzer Space Telescope will begin this summer.
Ultra-violet imaging using NASA's Galaxy Evolution Explorer (GALEX) satellite. These observations would cover the wavelength range of 0.1 to 0.3 microns.
Optical Spectroscopy and U-band (0.3 microns) imaging with the Visible Imaging Multi-Object Spectrograph (VIMOS) on the Melipal unit of the European Southern Observatory's (ESO) Very Large Telescope.
It is possible that SXDS will be one of the first survey fields for the Atacama Large Millimeter Array(ALMA) once it is operational. ALMA will obtain data in the 0.3-10 mm range (300 to 10000 microns).
Most deep surveys have been "pencil beam surveys" which look deeply into the Universe in a small piece of sky. Such surveys can show when different types of astronomical objects came into existence, but not how typical they are. The role different types of galaxies play in the larger picture of the evolution of the Universe, and their relationship to galaxies as they exist today remain largely unknown.
On very large scales, the Universe appears to be homogenouse and looks the same everywhere, but on scales of several tens of million light years, the Universe appears to have a foam like structure, with voids with few galaxies, and filaments or sheets where galaxies congregate. A pencil beam survey may point into a void or along a filament, and may not reveal the typical property of galaxies in the Universe. To understand the average properties of the Universe, a survey needs to cover scales that exceed several tens of millions of light years. Of course, even observing the entire sky would not be enough if the observations do not reveal the faintest most distant galaxies. Deep observations are necessary to study how galaxies have changed over time.
To study the history of galaxies, it is important to balance the size of the survey field and the depth of the observations. The SXDS survey field corresponds to a piece of the Universe about 150 million times 150 million light years in area in the Universe of 5 to 13 billion years ago. It samples of a volume of several billion cubic light years.
Almost all our knowledge of the Universe is derived from the measurement of light. Also known as electromagnetic radiation, light has different names depending on its wavelength: Gamma-rays, X-rays, UV-rays, visible light, infrared light, microwaves, sub-millimeter waves and radio waves (from short wavelength/high frequency/high energy to long wavelength/ low frequency/ low energy). At different wavelengths, light carries distinct information about its source such as distance, movement, temperature, density and chemical composition. Using modern technologies such as senstive infrared detectors and artificial satellites, astronomers are now able to explore the Univserse at most wavelengths.
Over a thousand X-ray sources are found in the XMM-Newton images. Some of them are nearby stars with a very active corona that radiates in the X-ray domain, but the largest majority are far flung active galaxies hiding powerful black holes in their nucleus. Other sources include distant clusters of galaxies, located up to eight thousand light years away. Since X rays travel in space at a finite speed, XMM-Newton gives us a view of these galaxies when they were much younger and less evolved than now. By comparing these images with those of nearby galaxies, astronomers can infer how they have evolved in the course of the last several thousand million years, or about three quarters of the life of the Universe.
The Subaru images of the SXDS field show a million galaxies of different colors in diverse envoronments. The visible color of a galaxy depend primarily on the age of its stars and its distance. A distant cluster of galaxies can easily be identified by the uniformly red color and small apparent size of their members. Many galaxies appear to belong to groups and may galaxies appear to be undergoin gravitational interactions with other galaxies. The colors, distribution, and appearance of the galaxies allow astronomers to trace how galaxies have been evolving with time.
The best way to determine the distance to a far away galaxy is spectroscopy. Spectroscopy involves dissecting light into different wavelengths and making a spectrum. Different molecules have characteristic wavelengths at which they emit and absorb light. When we observe a moving object, these characteristic wavelengths appear to shift in proportion to the speed at which they are moving away or towards us. When something is moving away from the observer, the wavelength shifts to longer wavelengths and appears redder. This is called a "redshift". Due to the expansion of the Universe, the farther away a galaxy is, the faster it is moving even further away. This means that a measurement of the redshift is a measurement of the distance to a galaxy or any other distant astronomical object.
Spectroscopy of very distant and faint galaxies is technologically very challenging, however. For example, it takes an hour of observing with the 8.2 meter effective aperture Subaru telescope to obtain a usable spectra of an object with a brightness of 23 magnitudes in visible light (several million times fainter than what can be observed with the naked eye). The faintest galaxies detected in the SXDS are 100 times fainter.
As an alternative, astronomers use a technique called "photometric redshift." As in the case with spectroscopy, shifts in characteristic features in a spectrum are sought as a measure of redshift, but instead of a fine dissection, the total amount of light in a specific wavelength ranges is measured by taking images of a galaxy with different filters. Although photometric redshifts are less precise and less accurate than spectroscopic redshifts, they are much easier to obtain for faint galaxies. In a large survey, the uncertainties in scientific conclusions based on the use of photometric redshifts is reduced by the number of galaxies that are under study.
Dr. Tadayuki Kodama used the visible data from Subaru/Suprime-Cam to select galaxies 8 billion light years away (in other words galaxies as they were 8 billion years ago when the universe was less than half of its current age) to see how they formed and how they may have evolved into galaxies of the present day Universe. He found that bright and massive galaxies and fainter and less massive galaxies form and evolve differently.
Galaxies that are heavier than 80 billion Suns have reddish colors indicating that they are made of old stars. Their distribution in space and the distribution of stars within them are comparable to elliptical galaxies in the present day universe. This implies that most elliptical galaxies must have already existed 8 billion years ago. On the other hand, galaxies with masses less than 10 billion Suns all had blueish colors indicative of young stars. These galaxies were still actively forming stars 8 billion years ago.
Such a scenario in which heavier galaxies evolve faster than lighter galaxies is called "down sizing". However, this scenario may contradict the currently most successful cosmological model of a universe filed with cold dark matter in which smaller objects form first. (This is called the bottom-up hypothesis.) These new results may force astronomers to look for a new physical mechanism that makes heavier objects form faster than our current cosmological model of the universe.
There will soon be near-infrared images of the SXDS field. By combining near-infrared information with the visible it will be possible to extend a similar analysis to more distant galaxies. This will allow scientists if down-sizing holds true at earlier times. it may also be possible to look back to the time when the higher mass galaxies were actively forming stars.
- Where can I find more information on the various telescopes that may be used to observe the SXDS field?
- ALMA (Atacama Large Millimeter Array)
http://www.alma.nrao.edu/ (NRAO site)
http://www.eso.org/projects/alma/ (ESO site)
http://www.nro.nao.ac.jp/alma/ (NAOJ site; Japanese only)
A large millimeter and sub-millimeter telescope combining 64 sensitive antennae and 16 supersensitive antennae each 12 meters in diameter. Now under construction in a high plateau in Chile 5000 meters in altitude. A collaboration of the United States , several European nations and Japan.
- BLAST (Balloon-borne Large-Aperture Sub-millimeter Telescope)
A balloon-borne sub-millimeter telescope with a 2-meter primary mirror developed by astronomers from the United Kingdom, the United States, mexico, and Canada.
- GALEX (Galaxy Evolution Explorer)
A UV satellite launched by NASA in April 2003.
- JCMT (James Clerk Maxwell Telescope)
A sub-millimeter telescope with a 15 meter aperture on Mauna Kea, Hawaii. Operated by the Joint Astronomy Centre, a collaboration of the United Kingdom, the Netherlands, and Canada.
- Spitzer Space Telescope
An infrared telescope launched by NASA in August 2003. One of NASA's four great space observatories which also include the Hubble Space Telescope, the Compton Gamma-ray Observatory and the Chandra X-ray Observatory.
- Subaru Telescope
An 8.2 meter effective aperture optical-infrared telescope operated by the National Astronomical Observatory of Japan.
- UKIRT (United Kingdom Infrared Telescope)
A 3.8m infrared telescope on Mauna Kea, Hawaii. The largest telescope that specializes in infrared observing. Operated by the Joint Astronomy Centre, a collaboration of the United Kingdom, the Netherlands, and Canada.
- VLA (Very Large Array)
A radio telescope in Socorro, New Mexico, consisting of 27 antennae each 25 meters in diameter.
- XMM-Newton (X-ray Multi-Mirror Mission - Newton)
An X-ray satellite launched by ESA in December , 1999. It has the largest aperture of all telescopes sensitive to X-rays in the 0.5-10 keV range (1/8000 to 1/400 microns).