From NOAJ Subaru: “Subaru Telescope Detects the Shadow of a Gas Cloud in an Ancient Proto-supercluster”

NAOJ

March 28, 2017

A team led by researchers from Osaka Sangyo University, with members from Tohoku University, Japan Aerospace Exploration Agency (JAXA) and others, has used the Suprime-Cam on the Subaru Telescope to create the most-extensive map of neutral hydrogen gas in the early universe (Figure 1). This cloud appears widely spread out across 160 million light-years in and around a structure called the proto-supercluster. It is the largest structure in the distant universe, and existed some 11.5 billion years ago. Such a huge gas cloud is extremely valuable for studying large-scale structure formation and the evolution of galaxies from gas in the early universe, and merits further investigation.

The distribution of galaxies in the proto-supercluster region 11.5 billion years ago (top left), and the Subaru Telescope Suprime-Cam image used in this work.

NAOJ Subaru Hyper Suprime Camera

Neutral hydrogen gas distribution is superposed on the Subaru image. The red color indicates denser regions of the neutral hydrogen gas. Cyan squares correspond to member galaxies in the proto-supercluster, while objects without cyan squares are foreground galaxies and stars. The distribution of neutral hydrogen gas does not align perfectly with the galaxies. (Credit: Osaka Sangyo University/NAOJ)

“We are surprised because the dense gas structure is extended much more than expected in the proto-supercluster,” said Dr. Mawatari. “Wider field observations with narrow-band filters are needed to grasp full picture of this largest structure in the young Universe. This is exactly the type of strong research that can be done with Hyper Suprime-Cam (HSC) recently mounted at the Subaru Telescope. We intend to study the gas – galaxy relation in various proto-superclusters using the HSC.”

Understanding Matter Distribution in the Universe

Stars assembled to form galaxies, and galaxies are clustered to form larger structures such as clusters or superclusters. Matter in the current universe is structured in a hierarchical manner on scales of ~ 100 million light-years. However, we cannot observe inhomogeneous structure in any direction or distance over scales larger than that. One important issue in modern astronomy is to clarify how perfectly the large-scale uniformity and homogeneity in matter distribution is maintained. In addition, astronomers seek to investigate the properties of the seeds of large-scale structures (i.e., the initial matter fluctuations) that existed at the beginning of the universe. Thus, it is important to observe huge structures at various epochs (which translates to distances). The study of gaseous matter as well as galaxies is needed for an accurate and comprehensive understanding. This is because local superclusters are known to be rich in gas. Furthermore, it is clear that there are many newborn galaxies in ancient (or distant) clusters. A detailed comparison between the spatial distributions of galaxies and gas during the early epochs of the universe is very important to understand process of galaxy formation from the dim (low light-emitting) clumps of gas in the early universe.

In order to investigate early, dim gas clouds, astronomers take advantage of the fact that light from bright distant objects gets dimmed by foreground gas (giving an effect like a “shadow picture”). Since neutral hydrogen in the gas cloud absorbs and dims light from background objects at a certain wavelength, we can see characteristic absorption feature in the spectrum of the background object. In many previous observations, researchers used quasars (which are very bright and distant) as background light sources. Because bright quasars are very rare, opportunities for such observations are limited. This allows astronomers to get information about the gas that lies only along the line of sight between a single QSO and Earth in a wide survey area. It has long been the goal to obtain “multi-dimensional” information of gas (e.g., spatially resolve the gas clouds) rather than the “one-dimensional” view currently available. This requires a new approach.

Expanding the View

To widen their view of these objects in the early universe, Dr. Ken Mawatari at Osaka Sangyo University and his colleagues recently developed a scheme to analyze the spatial distribution of the neutral hydrogen gas using imaging data of galaxies of the distant epoch (Figure 2).

Figure 2: Schematic pictures of an analysis scheme of previous work (left) and a new method (right). In the previous approach, basically a single background light source (quasar) can be used in a searched area. On the other hand, with the new scheme, it is easier to spatially resolve the neutral hydrogen gas density by using many normal galaxies in a searched area as background light sources. In the new scheme, absorption strength by the neutral hydrogen gas is estimated by measuring how much flux of the background galaxies becomes dimmed in the narrow-band image, not by using spectrum. By combining this scheme with the wide-area imaging ability of the Subaru Telescope, Mawatari, et al. made the most-extensive map of neutral hydrogen gas ever created. (Credit: Osaka Sangyo University/NAOJ)

There are two major advantages to this approach. First, instead of rare quasars, the team uses numerous normal galaxies as background light sources to investigate gas distribution at various places in the search area. Second, they use imaging data taken with the narrow-band filter on Suprime-cam. It is fine-tuned so that light with certain wavelengths can be transmitted, to capture evidence of absorption by the neutral hydrogen gas (the shadow picture effect). Compared with the traditional scheme of observations based on spectroscopy of quasars, this new method enables Mawatari and his collaborators to obtain wide-area gas distribution information relatively quickly.

The researchers applied their scheme to the Subaru Telescope Suprime-Cam imaging data taken in their previous large survey of galaxies. The fields investigated in this work include the SSA22 field, an ancestor of a supercluster of galaxies (proto-supercluster), where young galaxies are formed actively, in the universe 11.5 billion years ago in the early universe.

New Maps of Neutral Hydrogen Distribution

The researchers’ work resulted in very wide-area maps of the neutral hydrogen gas in the three fields studied (Figure 3).

Figure 3: Sky distribution of the neutral hydrogen gas in the three fields studied in this work. While in the normal fields (SXDS and GOODS-N) the neutral hydrogen gas density is consistent with the average density in the entire universe at 11.5 billion years ago, the neutral hydrogen gas density is higher than the average over the entire SSA22 proto-supercluster field. Contours correspond to the galaxies’ number density. Bold, solid thin, and dashed contours mean the average, high density, and low density regions, respectively. (Credit: Osaka Sangyo University/NAOJ)

It appears that the neutral hydrogen gas absorption is significantly strong over the entire SSA22 proto-supercluster field compared with those in the normal fields (SXDS and GOODS-N). It is clearly confirmed that the proto-supercluster environment is rich in neutral hydrogen gas, which is the major building block of galaxies.

The team’s work also revealed that gas distribution in the proto-supercluster region does not align with the galaxies’ distribution perfectly (see Figure 1 and Figure 3). While the proto-supercluster is rich in both galaxies and gas, there is no local-scale dependency of gas amount correlated with the density of galaxies inside the proto-supercluster. This result may mean that the neutral hydrogen gas not only is associated with the individual galaxies but also spreads out diffusely across intergalactic space only within the proto-supercluster. Since the neutral hydrogen gas excess in the SSA22 field is detected over the entire searched area, this overdense gas structure is actually extended more than 160 million light-years. In the traditional view of structure formation, matter density fluctuation is thought to be smaller and large-scale high-density structure was rarer in the early universe. The discovery that a gas structure that extends across more than 160 million light-years (which is roughly same as present-day superclusters in scale) already existed in the universe 11.5 billion years ago is a surprising result of this study.

By investigating spatial distribution of the neutral hydrogen gas in a very large area, the researchers have provided a new window on the relation between gas and galaxies in the young universe. The SSA22 huge gas structure revealed by this work is considered a key object to test the standard theory of structure formation, and so further investigation is anticipated.

This research will be published in the journal of the British Royal Astronomical Society (Monthly Notices of the Royal Astronomical Society, publisher Oxford University Press) in its June, 2017 issue of the printed version (Mawatari et al. 2017, MNRAS, 467, 3951, “Imaging of diffuse HI absorption structure in the SSA22 protocluster region at z = 3.1”). This work is supported by JSPS Grant-in-Aid JP26287034 and JP16H06713.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

Subaru

ALMA

Solar Flare Telescope

Nobeyama Radio Observatory

Nobeyama Radio Observatory: Solar

Mizusawa VERA Observatory

Okayama Astrophysical Observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

From NAOJ: “Saturn’s Rings Viewed in the Mid-infrared Show Bright Cassini Division”

NAOJ

Figure 1: A three-color composite of the mid-infrared images of Saturn on January 23, 2008 captured with COMICS on the Subaru Telescope. The Cassini Division and the C ring appear bright. Color differences reflect the temperatures; the warmer part is blue, the cooler part is red. (Credit: NAOJ)

A team of researchers has succeeded in measuring the brightnesses and temperatures of Saturn’s rings using the mid-infrared images taken by the Subaru Telescope in 2008. The images are the highest resolution ground-based views ever made. They reveal that, at that time, the Cassini Division and the C ring were brighter than the other rings in the mid-infrared light and that the brightness contrast appeared to be the inverse of that seen in the visible light (Figure 1). The data give important insights into the nature of Saturn’s rings.

The beautiful appearance of Saturn and its rings has always fascinated people. The rings consist of countless numbers of ice particles orbiting above Saturn’s equator. However, their detailed origin and nature remain unknown. Spacecraft- and ground-based telescopes have tackled that mystery with many observations at various wavelengths and methods. The international Cassini mission led by NASA has been observing Saturn and its rings for more than 10 years, and has released a huge number of beautiful images.

Subaru Views Saturn

The Subaru Telescope also has observed Saturn several times over the years. Dr. Hideaki Fujiwara, Subaru Public Information Officer/Scientist, analyzed data taken in January 2008 using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the telescope to produce a beautiful image of Saturn for public information purposes. During the analysis, he noticed that the appearance of Saturn’s rings in the mid-infrared part of the spectrum was totally different from what is seen in the visible light.

Saturn’s main rings consist of the C, B, and A rings, each with different populations of particles. The Cassini Division separates the B and A rings. The 2008 image shows that the Cassini Division and the C ring are brighter in the mid-infrared wavelengths than the B and A rings appear to be (Figure 1). This brightness contrast is the inverse of how they appear in the visible light, where the B and A rings are always brighter than the Cassini Division and the C ring (Figure 2).

Figure 2: Comparison of the images of Saturn’s rings in the 2008 view in the mid-infrared (left) and the visible light (right). The visible light image was taken on March 16, 2008 with the 105-cm Murikabushi telescope at Ishigakijima Astronomical Observatory. The radial brightness contrast of Saturn’s rings is the inverse between the two wavelength ranges. (Credit: NAOJ)

“Thermal emission” from ring particles is observed in the mid-infrared, where warmer particles are brighter. The team measured the temperatures of the rings from the images, which revealed that the Cassini Division and the C ring are warmer than the B and A rings. The team concluded that this was because the particles in the Cassini Division and C ring are more easily heated by solar light due to their sparser populations and darker surfaces.

On the other hand, in the visible light, observers see sunlight being reflected by the ring particles. Therefore, the B and A rings, with their dense populations of particles, always seem bright in the visible wavelengths, while the Cassini Division and the C ring appear faint. The difference in the emission process explains the inverse brightnesses of Saturn’s rings between the mid-infrared and the visible-light views.

Changing Angles Change the Brightnesses

Figure 3: Comparison of the mid-infrared images of Saturn’s rings on April 30, 2005 (top) and January 23, 2008 (bottom). Although both of the images were taken in the mid-infrared, the radial contrast of Saturn’s rings is the inverse of each other. (Credit: NAOJ)

The team concluded that the “inversion” of the brightness of Saturn’s rings between 2005 and 2008 was caused by the seasonal change in the ring opening angle to the Sun and Earth. Since the rotation axis of Saturn inclines compared to its orbital plane around the Sun, the ring opening angle to the Sun changes over a 15-year cycle. This makes a seasonal variation in the solar heating of the ring particles. The change in the opening angle viewed from the Earth affects the apparent filling factor of the particles in the rings. These two variations – the temperature and the observed filling factor of the particles – led to the change in the mid-infrared appearance of Saturn’s rings.

The data taken with the Subaru Telescope revealed that the Cassini Division and the C ring are sometimes bright in the mid-infrared though they are always faint in visible light. “I am so happy that the public information activities of the Subaru Telescope, of which I am in charge, led to this scientific finding,” said Dr. Fujiwara. “We are going to observe Saturn again in May 2017 and hope to investigate the nature of Saturn’s rings further by taking advantages of observations with space missions and ground-based telescopes.”

This research is published in Astronomy & Astrophysics, Volume 599, A29 and posted on-line on February 23, 2017 (Fujiwara et al., 2017, Seasonal variation of the radial brightness contrast of Saturn’s rings viewed in mid-infrared by Subaru/COMICS). This work is supported JSPS KAKENHI Grant Numbers JP23103002 and JP26800110.

The research team:

Hideaki Fujiwara: Subaru Telescope, National Astronomical Observatory of Japan, USA
Ryuji Morishima: University of California, Los Angeles/Jet Propulsion Laboratory, California Institute of Technology, USA
Takuya Fujiyoshi: Subaru Telescope, National Astronomical Observatory of Japan, USA
Takuya Yamashita: National Astronomical Observatory of Japan, Japan

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

Subaru

ALMA

Solar Flare Telescope

Nobeyama Radio Observatory

Nobeyama Radio Observatory: Solar

Mizusawa VERA Observatory

Okayama Astrophysical Observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

From Subaru: “Tracing the Cosmic Web with Star-forming Galaxies in the Distant Universe”

NAOJ

January 30, 2017
No writer credit

A research group led by Hiroshima University has revealed a picture of the increasing fraction of massive star-forming galaxies in the distant universe. Massive star-forming galaxies in the distant universe, about 5 billion years ago, trace large-scale structure in the universe. In the nearby universe, about 3 billion years ago, massive star-forming galaxies are not apparent. This change in the way star-forming galaxies trace the matter distribution is consistent with the picture of galaxy evolution established by other independent studies.

Figure 1: A close-up view of the cluster of galaxies observed. The image is a compotie of the i-band data (in red) from the Hyper Suprime-Cam at the Subaru Telescope and R-band (in green) and V-band (in blue) images from the Mayall 4-m telescope at the Kitt Peak National Observatory of National Optical Astronomy Observatory. Contour lines show the mass distribution. Red and blue circles show galaxies that stopped star formation and galaxies with star formation, respectively. The research team was able to study the evolution of the large scale structure in the Universe by comparing the mass distribution in the Universe and the distribution of the galaxies. (Credit: Hiroshima University/NAOJ)

Galaxies in the universe trace patterns on very large scales; there are large empty regions (called “voids”) and dense regions where the galaxies exist. This distribution is called the cosmic web. The most massive concentrations of galaxies are clusters. The formation of the cosmic web is governed by the action of gravity on the invisible mysterious “dark matter” that exists throughout the universe. The normal baryonic material one can see falls into the dark matter halos and forms galaxies. The action of gravity over about 14-billion-year history of the universe makes the halos cluster together. The location of galaxies or clusters in this enormous cosmic web tests our understanding of the way structure forms in the universe.

Increasingly, deeper and more extensive observations with telescopes like Subaru Telescope provide a clearer picture of the way galaxies evolve within the cosmic web. Of course, one cannot see the dark matter directly. However, one can use the galaxies that are seen to trace the dark matter. It is also possible to use the way the gravity of clusters of galaxies distort more distant background galaxies, weak gravitational lensing, as another tracer.

The Hiroshima group combined these two tracers: galaxies and their weak lensing signal to map the changing role of massive star-forming galaxies as the universe evolves.

Weak lensing is a phenomenon that provides a powerful technique for mapping the changing contribution of star-forming galaxies as tracers of the cosmic web. The cluster of galaxies and surrounding dark matter halo act as a gravitational lens. The lens bends the light passing through from more distant galaxies and distorts the images of them. The distortions of the appearance of the background galaxies provide a two-dimensional image of the foreground dark matter distribution that acts as a huge lens. The excellent imaging of the Subaru Telescope covering large regions of the sky provides exactly the data needed to construct maps of this weak lensing.

Dr. Yousuke Utsumi, a member of Hyper Suprime-Cam building team and a project assistant professor at Hiroshima University, conducted a 1-hour observation of a 4-deg2 patch of sky in the direction of the constellation Cancer. Figure 1 shows a close-up view of a cluster of galaxies with the weak lensing map tracing the matter distribution. The highest peaks in the maps correspond the foreground massive clusters of galaxies that lie 5 billion light-years away.

To map the three-dimensional distribution of the foreground galaxies, spectrographs on large telescopes like the 6.5-meter MMT disperse the light with a grating.

MMT Telescope at the summit of Mount Hopkins near Tucson, Arizona, USA

The expansion of the universe shifts the light to the red and by measuring this shift one measures the distances to the galaxies. Using spectroscopy places the galaxies in the cosmic web. The observations locate star-forming galaxies and those that are no longer forming stars.

Collaborators led by Dr. Margaret Geller (Harvard-Smithsonian Center for Astrophysics) conducted spectroscopic measurements for galaxies. The Hectospec instrument on the MMT enables measurements of redshifts for 250 galaxies at a time. The survey contains measurements for 12,000 galaxies.

The MMT redshift survey provides the map for the way all types of galaxies might contribute to the weak lensing map. Because the MMT survey provides distances to the galaxies, slices of the map at different distances corresponding to different epochs in the history of the universe can also be made and compared with the lensing map.

The MMT survey provides a predicted map of the cosmic web based on the positions of galaxies in three-dimensional space. Research team compared this map with the weak lensing map to discover the similarities. Figure 2 shows that both the highest peak and the largest empty regions are similar in the two maps. In other words, the matter distribution traced by the foreground galaxies and the distribution traced by the Subaru weak lensing map are similar. There are two complementary views of the cosmic web in this patch of the universe.

Figure 2: Distribution of mass (left) and galaxies (right) in the corresponding area. The conspicuous feature in the galaxy distribution also is visible in the left side, mass distribution, while the areas with no structure in the right also has no feature in the left. (Credit: Hiroshima University/NAOJ)

If they slice up the three-dimensional map in different redshift or time slices, they can examine the way the correspondence between these maps and the weak lensing map changes for different slices (Figure 3). Remarkably, the distribution of star-forming galaxies around a cluster of galaxies in the more distant universe (5 billion years ago) corresponds much more closely with the weak lensing map than a slice of the more nearby universe (3 billion years ago). In other words, the contribution of star-forming galaxies to the cosmic web is more prominent in the distant universe. These maps are the first demonstration of this effect in the weak lensing signal (Figure 4).

Figure 3: The distribution of galaxies with respect to the distance. The panels show the three-dimensional distribution of the galaxies, viewed from the observer on Earth. Red points represent quiescent galaxies and blue points are star-forming galaxies. Boxes in the cone are 3 and 5 billion light-years from the observer. The maps next to the enclosed areas show the corresponding distribution of galaxies. (Credit: Hiroshima University/NAOJ)

Figure 4: Close-ups of the cluster of galaxies at 3 billion light years (top) and 5 billion light years (bottom). These panels show the distribution of mass (left), quiescent galaxies (middle), and star forming galaxies (right), respectively. Three billion years ago, it is hard to see any similarity between the star-forming galaxies and the mass distribution, but there is much greater similarity in the maps of 5 billion years ago. (Credit: Hiroshima University/NAOJ)

The research team provides a new window on galaxy evolution by comparing the three-dimensional galaxy distribution mapped with a redshift survey including star-forming galaxies to a weak lensing map based on Subaru imaging.

“It turns out that the contribution of star-forming galaxies as tracers of the mass distribution in the distant universe is not negligible,” said Dr. Utsumi. “The HSC weak lensing map should contain signals from more distant galaxies in the 8 billion-year-old universe. Deeper redshift surveys combined with similar weak lensing maps should reveal an even greater contribution of star-forming galaxies as tracers of the matter distribution in this higher redshift range. Using the next generation spectrograph for the Subaru Telescope, Prime Focus Spectrograph (PFS), we hope to extend our maps to the interesting era.”

NAOJ Subaru Prime Focus Spectrograph

This research is published in the Astrophysical Journal in its December 14, 2016 on-line version and December 20, 2016 in the printed version, Volume 833, Number 2. The title of the paper is A weak lensing view of the downsizing of star-forming galaxies by Y. Utsumi et al., which is also available in preprint from arXiv:1606.07439v2. This work is supported by a JSPS Grant-in-Aid for Young Scientists (B) (JP26800103) and a MEXT Grant-in-Aid for Scientific Research on Innovative Areas (JP24103003).

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

Subaru

ALMA

Solar Flare Telescope

Nobeyama Radio Observatory

Nobeyama Radio Observatory: Solar

Mizusawa VERA Observatory

Okayama Astrophysical Observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

From EarthSky: “New record-breaking Milky Way satellite”

EarthSky

November 21, 2016
Deborah Byrd

It’s record-breaking because it’s so faint. Could this galaxy be a sign of many yet-unknown dwarf galaxies orbiting our Milky Way? And do we now have a way to detect them? Astronomical theorists hope so!

Satellite galaxies associated with the Milky Way, which is shown here as the gray oval in the center of the diagram. Squares are Large and Small Magellanic Clouds and circles are dwarf spheroidal galaxies. Via subarutelescope.org.

NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA

An international team led by astronomers from Tohoku University in Japan said on November 21, 2016 that it has found an extremely faint dwarf satellite galaxy orbiting the center of our Milky Way galaxy. They’ve named the satellite Virgo I, because it lies in the direction of the constellation Virgo the Maiden. The galaxy is very faint, perhaps the faintest satellite galaxy yet found. Its discovery suggests the presence of a large number of yet-undetected dwarf satellites in the halo of the Milky Way. That would be good news to astronomical theorists, whose leading theories about our universe require many more dwarf galaxies for our Milky Way and other galaxies than have been observed so far.

The team’s discovery is part of the ongoing Subaru Strategic Survey using a gigantic digital still camera called Hyper Suprime-Cam.

NAOJ Subaru Hyper Suprime-Cam

Astronomers have been pondering the puzzle of dwarf galaxies for some years. Standard cosmology predicts there should be hundreds of dwarf galaxies in orbit around galaxies like our Milky Way galaxy. But, so far, astronomers know of only about 50 small galaxies within about 1.4 million light-years of the Milky Way, and it’s possible they’re not all true Milky Way satellites. A statement issued by Tohoku University astronomers on November 21, 2016 explained:

“Formation of galaxies like the Milky Way is thought to proceed through the hierarchical assembly of dark matter, forming dark halos, and through the subsequent infall of gas and star formation affected by gravity. Standard models of galaxy formation in the context of the so-called cold dark matter (CDM) theory predict the presence of hundreds of small dark halos orbiting in a Milky Way-sized dark halo and a comparable number of luminous satellite companions. However, only tens of satellites have ever been identified. This falls well short of a theoretical predicted number, which is part of the so-called missing satellite problem.”

In other words, if what we think we understand about the universe is correct, where are the rest of the dwarf galaxies?

About 40 of the 50 known dwarf galaxies orbiting our Milky Way belong to a category that astronomers call dwarf spheroidal galaxies. However, many recently discovered dwarf galaxies are much fainter. These are called ultra-faint dwarf galaxies by astronomers. Obviously, the much-fainter ones are much harder to detect. So one idea has been that the dwarf galaxies are there, and we just haven’t seen them yet.

If that’s the case, then the detection of Virgo 1 might be a sign we can now detect much-fainter galaxies than before. If so, astronomers might begin detecting many more of them.

And, if that happens, many astronomical theorists will be glad! It’ll mean their theories are on the right track.

white -> yellow -> red indicates increasing density. (Credit: Tohoku University/National Astronomical Observation of Japan/ subarutelescope.org.” width=”800″ height=”340″ class=”size-full wp-image-251652″ /> The position of Virgo I in the constellation of Virgo the Maiden (left). Image via Tohoku University/ National Astronomical Observation of Japan/ subarutelescope.org.

Astronomy graduate studentDaisuke Homma Tohoku University made the discovery. He commented:

“We have carefully examined the early data of the Subaru Strategic Survey with HSC and found an apparent over density of stars in Virgo with very high statistical significance … Surprisingly, this is one of the faintest satellites, with absolute magnitude of -0.8 in the optical waveband.”

Homma worked under the guidance of his advisor, Masashi Chiba, and their international collaborators. According to Chiba, the discovery has profound implications:

This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way.

How many satellites are indeed there and what properties they have, will give us an important clue of understanding how the Milky Way formed and how dark matter contributed to it.

The team’s finding is published in the peer-reviewed Astrophysical Journal in its November 14, 2016 on-line version and November 20, 2016 in the printed version.

Bottom line: Astronomers said on November 21, 2016 that they’ve found a record-breakingly faint dwarf satellite galaxy orbiting the center of our Milky Way galaxy. They’ve named the satellite Virgo I. It might be a sign that many more faint galaxies like this one orbit the Milky Way, and, if so, it will help confirm leading astronomical theories.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

From phys.org: “Astronomers discover new substellar companion to the Pleiades member star”

phys.org

August 10, 2016
Tomasz Nowakowsk

Final Pleiades HII 3441 images. (Left) reduced HS -band image taken in the 2011 observation. (Middle) reduced HL-band image taken in the 2011 observation. (Right) reduced H-band image taken in the 2014 observation. All images were analyzed using standard ADI. Pleiades HII 3441B can be seen southeast of the primary star. There is no methane absorption in Pleiades HII 3441B when left and middle panels are compared. Credit: Konishi et al., 2016.

An international team of astronomers has found a new substellar mass companion to one of the stars in the Pleiades open cluster. The discovery could contribute to our understanding of stellar and substellar multiplicity as well as formation mechanisms in this cluster. A study detailing the new findings was published Aug. 5 on the arXiv pre-print server.

Due to its proximity, the well-known Pleiades cluster is frequently observed and studied by amateur and professional astronomers. The cluster, located some 440 light years away, is about 120 million years old, which makes it one of the nearest young open clusters. It is also a great target for searching new low-mass substellar objects such as brown dwarfs.

From 2011 to 2015, an international team of researchers led by Mihoko Konishi of the National Astronomical Observatory of Japan conducted a series of observations of the cluster’s member star, designated Pleiades HII 3441, looking for planetary-mass and substellar companions. These observations were part of the Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS) survey, which uses adaptive optics assisted high contrast imaging for studying planets and disks, including primordial systems, transitional systems and mature systems. The survey utilizes the 8.2 Subaru Telescope located on Mauna Kea, Hawaii.

NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA

The newly detected object was named Pleiades HII 3441B. According to the study, it was found southeast of the primary star with a projected separation of about 66 AU.

“A companion candidate was detected southeast of the primary star, and subsequently confirmed as a companion object to the primary star. (…) The projected separation and position angle are 0.′′49 ± 0.′′02 (66 ± 2 AU) and 136.4° ± 3.2°, respectively. These values were derived by averaging all observations,” the researchers wrote in the paper.

The mass of Pleiades HII 3441B was calculated to be approximately 68 Jupiter masses and its temperature was estimated to be 2,700 K. Moreover, the team found that there is no methane absorption in the atmosphere of this substellar companion. They emphasized that methane is considered to condense below 1,300 K.

The object was classified an M7-type brown dwarf, due to the fact that its mass is below the hydrogen-burning limit (72 Jupiter masses). Its spectral type was deducted from the photometry-derived temperature. However, as the researchers noted, Pleiades HII 3441B is “close to the boundary between the stellar and substellar regime.”

The scientists have also taken into account the possibility that the object is another faint Pleiades member along the same line of sight; it cannot be ruled out completely as the observations could not detect the orbital motion.

According to the researchers, their study provides an important input for the determination of the initial mass function in Pleiades, and might help us understand the formation mechanisms in the cluster. Substellar multiplicity in Pleiades is also discussed in the paper, with the aim to estimate the general fraction of substellar companions in star clusters. However, as the team noted, further studies are needed in order to get comprehensive answers.

“A much larger survey of the Pleiades would be needed to draw general conclusion on the multiplicity differences between open clusters and field star populations,” the astronomers concluded.

Read more at: http://phys.org/news/2016-08-astronomers-substellar-companion-pleiades-member.html#jCp

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

About Phys.org in 100 Words

Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

From NAOJ Subaru: “Ancient Eye in the Sky”

NAOJ

July 25, 2016
No writer credit found

Light from a distant galaxy can be strongly bent by the gravitational influence of a foreground galaxy. That effect is called strong gravitational lensing. Normally a single galaxy is lensed at a time. The same foreground galaxy can – in theory – simultaneously lens multiple background galaxies. Although extremely rare, such a lens system offers a unique opportunity to probe the fundamental physics of galaxies and add to our understanding of cosmology. One such lens system has recently been discovered and the discovery was made not in an astronomer’s office, but in a classroom. It has been dubbed the Eye of Horus (Fig. 1), and this ancient eye in the sky will help us understand the history of the universe.

Figure 1: Eye of Horus in pseudo color. Enlarged image to the right (field of view of 23 arcseconds x 19 arcseconds) show two arcs/rings with different colors. The inner arc has a reddish hue, while the outer arc has a blue tint. These arcs are lensed images of the two background galaxies. There are blobs in and around the arcs/rings, which are also the lensed images of those background galaxies. The yellow-ish object at the center is a massive galaxy at z = 0.79 (distance 7 billion light years), which bends the light from the two background galaxies. The wide field image in the background is here. Enlarged image of the Eye of Horus is here and the image with labels is here. (Credit: NAOJ)

Classroom Research Pays Off

Subaru Telescope organizes a school for undergraduate students each year. One such session was held in September 2015 at the NAOJ headquarters in Mitaka, Tokyo (Fig. 2). Subaru is currently undertaking a massive survey to image a large area of the sky at an unprecedented depth with Hyper Suprime-Cam as part of the Subaru Strategic Program. A group of astronomers and young students were analyzing some of that Hyper Suprime-Cam data at the school when they found a unique lens system. It was a classic case of a serendipitous discovery.

“When I was looking at HSC images with the students, we came across a ring-like galaxy and we immediately recognized it as a strong-lensing signature,” said Masayuki Tanaka, the lead author of a science paper on the system’s discovery. “The discovery would not have been possible without the large survey data to find such a rare object, as well as the deep, high quality images to detect light from distant objects.”

Arsha Dezuka, a student who was working on the data, was astonished at the find. “It was my first time to look at the astronomical images taken with Hyper Suprime-Cam and I had no idea what the ring-like galaxy is,” she said. “It was a great surprise for me to learn that it is such a rare, unique system!”

What They Saw

A close inspection of the images revealed two distinct arcs/rings of light with different colors. This strongly suggested that two distinct background galaxies were being lensed by the foreground galaxy. The lensing galaxy has a spectroscopic redshift of z = 0.79 (which means it’s 7.0 billion light-years away, Note 1) based on data from the Sloan Digital Sky Survey. Follow-up spectroscopic observations of the lensed objects using the infrared-sensitive FIRE spectrometer on the Magellan Telescope confirmed that there are actually two galaxies behind the lens. One lies at z = 1.30 and the other is at z = 1.99 (9.0 and 10.5 billion light-years away, respectively).

“The spectroscopic data reveal some very interesting things about the background sources,” said Kenneth Wong from NAOJ, the second author of the scientific paper describing the system. “Not only do they confirm that there are two sources at different distances from us, but the more distant source seems to consist of two distinct clumps, which could indicate an interacting pair of galaxies. Also, one of the multiple images of that source is itself being split into two images, which could be due to a satellite galaxy that is too faint for us to see.”

The distinct features for the system (several bright knots, an arc, a complete Einstein ring) arise from the nice alignment of the central lens galaxy and both sources, creating an eye-like structure (Fig.3). The astronomers dubbed it Eye of Horus, for the sacred eye of an ancient Egyptian god, since the system has an uncanny resemblance to it.

Figure 3: A schematic diagram showing the location of galaxies creating the gravitational lens effect of Eye of Horus. A galaxy 7 billion light years from the Earth bends the light from the two galaxies behind it at a distance of 9 billion light years and 10.5 billion light years, respectively. (Credit: NAOJ)

The survey with Hyper Suprime-Cam is only 30% complete and it will collect data for several more years. Astronomers expect to find roughly 10 more such systems in the survey, which will provide important insights into the fundamental physics of galaxies as well as how the universe expanded over the last several billion years.

This research was supported by JSPS KAKENHI Grant Numbers JP15K17617, JP26800093, and JP15H05892. The research paper appeared on-line in the Astrophysical Journal Letters on July 25, 2016.

Note:
1. Conversion of the distance from the redshift uses the following cosmological parameters – H0=67.3km/s/Mpc, Ωm=0.315, Λ=0.685, based on Planck 2013 Results.

Research Team

Masayuki Tanaka: National Astronomical Observatory of Japan, Japan
Kenneth Wong: National Astronomical Observatory of Japan, Japan
Anupreeta More: Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo, Japan
Arsha Dezuka: Department of Astronomy, University of Kyoto, Japan
Eiichi Egami: Steward Observatory, University of Arizona, USA
Masamune Oguri: Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo, Japan; Department of Physics, University of Tokyo, Japan; Research Center for the Early Universe, University of Tokyo, Japan
Sherry H. Suyu: Max Planck Institute for Astrophysics, Germany; Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan
Alessandro Sonnenfeld: Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo, Japan
Ryou Higuchi: Institute for Cosmic Ray Research, The University of Tokyo, Japan
Yutaka Komiyama: National Astronomical Observatory of Japan, Japan
Satoshi Miyazaki: National Astronomical Observatory of Japan, Japan; SOKENDAI (The Graduate University for Advanced Studies), Japan
Masafusa Onoue: SOKENDAI (The Graduate University for Advanced Studies), Japan; National Astronomical Observatory of Japan, Japan
Shuri Oyamada: Japan Women’s University, Japan
Yousuke Utsumi: Hiroshima Astrophysical Science Center, Hiroshima University, Japan

See the full article here .
See the IPMU article here .

Please help promote STEM in your local schools.

Stem Education Coalition
The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

Subaru

ESO/NRAO/NAOJ ALMA Array

Solar Flare Telescope

Nobeyama Radio Observatory

Nobeyama Radio Observatory: Solar

Mizusawa VERA Observatory

Okayama Astrophysical Observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

From IPMU: “New test by deepest galaxy map finds Einstein’s theory stands true”

The Kavli Foundation

Kavli IMPU

May 11, 2016
Media contact:
Motoko Kakubayashi
Press Officer
Kavli Institute for the Physics and Mathematics of the Universe
The University of Tokyo Institutes for Advanced Study,
The University of Tokyo
TEL: +81-04-7136-5980
E-mail: press@ipmu.jp

Research contact:
Teppei Okumura
Project Researcher
Kavli Institute for the Physics and Mathematics of the Universe
TEL: +81-04-7136-6539
E-mail: teppei.okumura@ipmu.jp

Chiaki Hikage
Project Assistant Professor
Kavli Institute for the Physics and Mathematics of the Universe
TEL: +81-04-7136-6532
E-mail: chiaki.hikage@ipmu.jp

Tomonori Totani
Professor
Department of Astronomy, University of Tokyo
TEL: +81-03-5841-4257
E-mail: totani@astron.s.u-tokyo.ac.jp

Image 1: A 3D map of the Universe spanning 12 to 14.5 billion light years (Credit: NAOJ; Partial data supplied by: CFHT, SDSS)

NAOJ/Subaru, Mauna Kea Hawaii, USA, and FMOS on Subaru used in this study.

CFHT, Mauna Kea Hawaii, USA

SDSS Telescope at Apache Point, NM, USA

An international team led by Japanese researchers has made a 3D map of 3000 galaxies 13 billion light years from Earth, and found that Einstein’s general theory of relativity is still valid.

Since it was discovered in the late 1990s that the universe is expanding at an accelerated rate, scientists have been trying to explain why. The mysterious dark energy could be driving acceleration, or Einstein’s theory of general relativity, which says gravity warps space and time, could be breaking down.

To test Einstein’s theory, a team of researchers led by Kavli Institute for the Physics and Mathematics (Kavli IPMU) Project Researcher Teppei Okumura, Kavli IPMU Project Assistant Professor Chiaki Hikage, University of Tokyo Department of Astronomy Professor Tomonori Totani, and together with Tohoku University Astronomical Institute Associate Professor Masayuki Akiyama and Kyoto University Department of Astronomy Associate Professor Fumihide Iwamuro and Professor Kouji Ohta, used FastSound Survey data on more than 3000 distant galaxies to analyze their velocities and clustering.

Their results indicated that even far into the universe, general relativity is valid, giving further support that the expansion of the universe could be explained by a cosmological constant, as proposed by Einstein in his theory of general relativity.

“We tested the theory of general relativity further than anyone else ever has. It’s a privilege to be able to publish our results 100 years after Einstein proposed his theory,” said Okumura.

“Having started this project 12 years ago it gives me great pleasure to finally see this result come out,” said Karl Glazebrook, Professor at Swinburne University of Technology, who proposed the survey.

No one has been able to analyze galaxies more than 10 billion light years away, but the team managed to break this barrier thanks to the FMOS (Fiber Multi-Object Spectrograph) on the Subaru Telescope, which can analyze galaxies 12.4 to 14.7 billion light years away. The Prime Focus Spectrograph, currently under construction, is expected to be able to study galaxies even further away.

Details of this study were published* online on April 27 in the Publications of the Astronomical Society of Japan.

Image 2: Experimental results looking at the expansion of the universe, in comparison to that predicted by Einstein’s theory of general relativity in green. (Credit: Okumura et al.)

*Science paper:
The Subaru FMOS galaxy redshift survey (FastSound). IV. New constraint on gravity theory from redshift space distortions at z∼1.4

Useful links
All images can be downloaded from this page: http://web.ipmu.jp/press/201605-fastsound

About the FastSound (FMOS Acceleration Samping Test Subaru Observation Understanding Nature of Dark energy) Survey: http://www.kusastro.kyoto-u.ac.jp/Fastsound/index.html

About the Prime Focus Spectrograph: http://pfs.ipmu.jp/

Video of the FastSound Survey map (Japanese text): https://www.youtube.com/watch?v=FSsjQsjOQDw

See the full article here .

Please help promote STEM in your local schools.

Kavli IPMU (Kavli Institute for the Physics and Mathematics of the Universe) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/
Stem Education Coalition
The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

From NAOJ: “Formation of a Rich Galaxy Cluster 7 Billion Years Ago”

NAOJ

May 10, 2016
Text by: Tadayuki Kodama (Subaru Telescope)
Translation by: Ramsey Lundock (NAOJ)

Galaxies tend to be clustered in space; these groups are called galaxy clusters.

This image is a small part (1 percent) of a photo which captured the appearance of a rich cluster at a time when the Universe was half its present age, in other words 7 billion years ago. Each of the image’s edges corresponds to about 4.5 million light-years. The majority of the reddish galaxies belong to this galactic cluster, forming a chain-like structure composed of 3 main clumps stretching in a southwesterly direction, starting from the upper left of the image.

It is thought that these clumps are attracted to each other through their mutual gravitational interactions, so that before long they will merge together, evolving into a single large cluster of galaxies. Here, we are witnessing the first stage in this process.

Panoramic View of an Ancient Celestial City

This image, taken as part of a research project (PISCES, representative: Kodama) to capture panoramic images of the formation of galaxy clusters and the evolution of the galaxies within them by using the Subaru Telescope, is the appearance of the central region of a rich galaxy cluster at a time when the Universe was approximately half its current age, about 7 billion years ago.

Each side of the image corresponds to approximately 4.5 million light-years, in other words twice the distance between our Milky Way Galaxy and the neighboring Andromeda Galaxy.

But hundreds of galaxies are crowded into this limited area. We found that the majority of the reddish galaxies belong to this galactic cluster, forming a chain-like structure composed of 3 main clumps stretching from the north-east (upper left in the image) to the south-west (lower right). It is thought that clumps of galaxies attract each other through gravity along this kind of chain structure, gathering and merging, evolving into a larger structure; that is to say we are seeing the formation site of a rich galaxy cluster.

Thanks to the Subaru Telescope’s unique large-format camera, many original results have been obtained. Research into large celestial structures like galaxy clusters is one of them. Now, a new even-larger format camera boasting 7 times the field of view has started operations. We expect research into these kinds of large-scale structures in the distant Universe to advance at an ever quickening pace.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

Subaru

ESO/NRAO/NAOJ ALMA Array

Solar Flare Telescope

Nobeyama Radio Observatory

Nobeyama Radio Observatory: Solar

Mizusawa VERA Observatory

Okayama Astrophysical Observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

From NAOJ: “Deciphering Compact Galaxies in the Young Universe”

NAOJ

March 7, 2016

A group of researchers using the Suprime-Cam instrument on the Subaru Telescope has discovered about 80 young galaxies that existed in the early universe about 1.2 billion years after the Big Bang.

Hyper Suprime-Cam

The team, with members from Ehime University, Nagoya University, Tohoku University, Space Telescope Science Institute (STScI) in the U.S., and California Institute of Technology, then made detailed analyses of imaging data of these galaxies taken by the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope.

ACS

NASA/ESA Hubble

At least 54 of the galaxies are spatially resolved in the ACS images. Among them, 8 galaxies show double-component structures, and the remaining 46 seem to have elongated structures. Through a further investigations using a computer simulation, the group found that the observed elongated structures can be reproduced if two or more galaxies reside in close proximity to each other.

These results strongly suggest that 1.2 billion years after the Big Bang, galactic clumps in the young universe grow to become large galaxies through mergers, which then causes active star formation to take place. This research was conducted as part of the treasury program of Hubble Space Telescope (HST), [Caltech] Cosmic Evolution Survey (COSMOS). The powerful survey capability of the Subaru Telescope provided the essential database of the candidate objects in the early universe for this research project.

The Importance of Studying Early Galaxies

In the present universe, at a point 13.8 billion years after the Big Bang, there are many giant galaxies like our Milky Way, which contains about 200 billion stars in a disk a hundred thousand light years across. However, there were definitely no galaxies like it in the epoch just after the Big Bang.

Pre-galactic clumps appear to have formed in the universe about 200 million years after the Big Bang. These were cold gas clouds much smaller than the present giant galaxies by a factor of 100, with masses smaller by a factor of a million. The first galaxies were formed when the first stars were born in these gas clumps. These small galactic clumps then experienced continuous mergers with surrounding clumps and eventually grew into large galaxies.

Much effort has been made through deep surveys to detect actively star-forming galaxies in the young universe. As a result, the distances of the earliest galaxies are now known to be at more than 13 billion light-years. We see them at a time when the age of the universe was only 800 million years (or about 6% of the present age). However, since most of the galaxies in the young universe were quite small, their detailed structures have not yet been observed.

Exploring the Young Universe Using Subaru Telescope and Hubble Space Telescope

While the wide field of view of the Subaru Telescope has played an important role in finding such young galaxies, the high spatial resolution of the Hubble Space Telescope (HST) is required to investigate the details of their shapes and internal structures. The research team looked back to a point 12.6 billion years ago using a two-pronged approach. The first step was to use the Subaru Telescope in a deep survey to search out the early galaxies, and then follow that up to investigate their shapes using the Advanced Camera for Surveys (ACS) on board the HST. The ACS revealed 8 out of 54 galaxies to have double-component structures, where two galaxies seem to be merging with each other (Note 1).

Then, a question arose as to whether the remaining 46 galaxies are really single galaxies. Here, the research team questioned why many of these galaxies show elongated shapes in the HST/ACS images. This is because such elongated shapes, together with the positive correlation between ellipticity (Note 2) and size strongly suggest a possibility that two small galaxies reside so close to each other that they cannot be resolved into two distinct galaxies, even using ACS.

To examine whether the idea of closely crowded galaxies is viable, the researchers conducted so-called Monte Carlo computer simulations. First, the group put two identical artificial sources at random locations with various angular separations onto the real observed ACS image. Then, the group tried to extract the images with the same method used for the actual observed ACS image and measured their ellipticities and sizes.

The simulated distribution reproduces the observed results very well. That is, most of the galaxies that were observed as single sources in the HST/ACS images are actually two merging galaxies. However, the distances between two merging galaxies are so small they cannot be spatially resolved, even by HST’s high resolution!

If this idea is valid for the galaxies that appear to be single, then it’s possible to assume that the galaxies with the highest rate of activities have the smallest sizes. This is expected because the smallest sizes imply the smallest separation between two merging galaxies. If this is the case, such galaxies would experience intense star formation activity triggered by their mergers.

On the other hand, some galaxies with the smallest sizes are moderately separated pairs, but are observed along the line of sight, or are just single, isolated star-forming galaxies. These are basically the same as large-size galaxies.

The research team has confirmed that the observed relation between star formation activity and size is consistently explained by the team’s idea.

To date, the shapes and structures of small young galaxies have been investigated by using ACS on HST. If a source was detected as a single ACS source, it was treated as a single galaxy and its morphological parameters were evaluated. This research suggests that such a small galaxy can consist of two (or perhaps, more) interacting/merging galaxies located so close together that they cannot be resolved by even the high angular resolution of the ACS.

Looking into the Future of Studying the Past

Current galaxy formation theories predict that small galaxies in the young universe evolve into large galaxies via successive mergers. The question remains: what is the next step in observational studies for galaxy formation in the young universe? This is one of the frontier fields that requires future “super telescopes,” e.g. Thirty Meter Telescope (TMT) and the James Webb Space Telescope (JWST). They will enable the next breakthroughs in the study of early galaxy formation and evolution.

This research will be published in the Astrophysical Journal titled “Morphological Properties of Lyman Alpha Emitters at Redshift 4.86 in the COSMOS Field: Clumpy Star Formation or Merger?” by Masakazu A. R. Kobayashi, Katsuhiro L. Murata, Anton M. Koekemoer, Takashi Murayama, Yoshiaki Taniguchi, Masaru Kajisawa, Yasuhiro Shioya, Nick Z. Scoville, Tohru Nagao, and Peter L. Capak. Online version was posted February 24, 2016 and print version was on March 1, 2016 (Volume 819, article id. 25).

Note:

1.A mean size (that is, a mean diameter of the circle which encloses half of the total light of galaxy) of individual small galaxies is about 5.5 thousand light-years (kly). A mean distance between the two small galaxies, which is projected distance on the sky, is 13 kly (13,000 light-years).
2.Ellipticity is defined as 1 – b/a, where a and b represent the major and minor radii of an ellipse. In the case of a circle, ellipticity is equal to zero because a equals to b. A more elongated shape results in a larger ellipticity.

Authors:

Masakazu A. R. Kobayashi: Research Center for Space and Cosmic Evolution, Ehime University, Japan
Katsuhiro L. Murata: Department of Physics, Nagoya University, Japan
Anton M. Koekemoer: Space Telescope Science Institute, USA
Takashi Murayama: Astronomical Institute, Graduate School of Science, Tohoku University, Japan
Yoshiaki Taniguchi: Research Center for Space and Cosmic Evolution, Ehime University, Japan
Masaru Kajisawa: Research Center for Space and Cosmic Evolution and Graduate School of Science and Engineering, Ehime University, Japan
Yasuhiro Shioya: Research Center for Space and Cosmic Evolution, Ehime University, Japan
Nick Z. Scoville: Department of Astronomy, California Institute of Technology, USA
Tohru Nagao: Research Center for Space and Cosmic Evolution, Ehime University, Japan
Peter L. Capak: Department of Astronomy and Spitzer Science Center, California Institute of Technology, USA

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

Subaru

ALMA

Solar Flare Telescope

Nobeyama Radio Observatory

Nobeyama Radio Observatory: Solar

Mizusawa VERA Observatory

Okayama Astrophysical Observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

From NAOJ/Subaru: “Subaru-HiCIAO Spots Young Stars Surreptitiously Gluttonizing Their Birth Clouds”

NAOJ

February 24, 2016
No writer credit found

An international team led by researchers at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has used a new infrared imaging technique to reveal dramatic moments in star and planet formation. These seem to occur when surrounding material falls toward very active baby stars, which then feed voraciously on it even as they remain hidden inside their birth clouds. The team used the HiCIAO (High Contrast Instrument for the Subaru Next-Generation Adaptive Optics) camera on the Subaru 8-meter Telescope in Hawaii to observe a set of newborn stars. The results of their work shed new light on our understanding of how stars and planets are born.

NAOJ Subaru HiCIAO Camera

A schematic diagram of star and planet formation based on Green (2001). (Credit: ASIAA)

The Process of Star Birth

Stars are born when giant clouds of dust and gas collapse under the pull of their own gravity. Planets are believed to be born at nearly the same time as their stars in the same disk of material. However, there are still a number of mysteries about the detailed physical processes that occur as stars and planets form.

The giant collections of dust and gas where stars form are called “molecular clouds” because they are largely made up of molecules of hydrogen and other gases. Over time, gravity in the densest regions of these clouds gathers in the surrounding gas and dust, via a process called “accretion”. It is often assumed that this process is smooth and continuous.

However, this steady infall explains only a small fraction of the final mass of each star that is born in the cloud. Astronomers are still working to understand when and how the remaining material is gathered in during the process of star and planet birth.

A few stars are known to be associated with a sudden and violent “feeding” frenzy from inside their stellar nursery. When they gluttonize on the surrounding material, their visible light increases very suddenly and dramatically, by a factor of about a hundred. These sudden flareups in brightness are called “FU Orionis outbursts” because they were first discovered toward the star FU Orionis.

Not many stars are found to be associated with such outbursts — only a dozen out of thousands. However, astronomers speculate that all baby stars may experience such outbursts as part of their growth. The reason we only see FU Ori outbursts toward a few newborn stars is simply because they are relatively quiet most of the time.

One key question about this mysterious facet of starbirth is “What are the detailed physical mechanisms of these outbursts?” The answer lies in the region surrounding the star. Astronomers know the optical outbursts are associated with a disk of material close to the star, called the accretion disk. It becomes significantly brighter when the disk gets heated up to temperatures similar to those of lava flows here on Earth (around 700 to 1200 C or 1292 to 2182 F) like the one flowing from Kilauea volcano area in the island of Hawaii. Several processes have been proposed as triggers for such outbursts and astronomers have been investigating them over the past few decades.

Finding a Mechanism for FU Ori Outbursts

An international team lead by Drs. Hauyu Baobab Liu and Hiro Takami, two researchers at ASIAA, used a novel imaging technique available at the Subaru Telescope to tackle this issue. The technique – imaging polarimetry with coronagraphy – has tremendous advantages for imaging the environments in the disks. In particular, its high angular resolution and sensitivity allow astronomers to “see” the light from the disk more easily. How does this work?

Circumstellar material is a mixture of gas and dust. The amount of dust is significantly smaller than the amount of gas in the cloud, so it has little effect on the motion of the material. However, dust particles scatter (reflect) light from the central star, illuminating all the surrounding material. The HiCIAO camera mounted on the Subaru 8.2-meter telescope, one of the largest optical and near-infrared (NIR) telescopes in the world, is well-suited to observing this dim circumstellar light. It successfully allowed the team to observe four stars experiencing FU Ori outbursts.

Details of Four FU Ori Outbursts

The team’s target stars are located 1,500-3,500 light-years from our solar system. The images of these outbursting newborns were surprising and fascinating, and nothing like anything previously observed around young stars. Three have unusual tails. One shows an “arm”, a feature created by the motion of material around the star. Another shows odd spiky features, which may result from an optical outburst blowing away circumstellar gas and dust. They show a messy and chaotic environment, much like a human baby eating food.

To understand the structures observed around these newborn stars, theorists on the team extensively studied one of several mechanisms proposed to explain FU Ori outbursts. It suggests that gravity in circumstellar gas and dust clouds creates complicated structures that look like cream stirred into coffee. These oddly shaped collections of material fall onto the star at irregular intervals. The team also conducted further computer simulations for scattered light from the outburst. Although more simulations are required to match the simulations to the observed images, these images show that this is a promising explanation for the nature of FU Ori outbursts.

Studying these structures may also reveal how some planetary systems are born. Astronomers know some exoplanets (planets around other stars) are found extremely far away from their central stars. Sometimes they orbit more than a thousand times the distance between the Sun and Earth, and significantly larger than the orbit of Neptune (which is about 30 times the distance between the Sun and Earth). These distances are also much larger than orbits explained by standard theories of planet formation. Simulations of complicated circumstellar structures like the ones seen in the HiCIAO views also predict that some dense clumps in the material may become gas giant planets. This would naturally explain the presence of exoplanets with such large orbits.

In spite of these exciting new results, there is a still great deal more work to do to understand the mechanisms of star and planet birth. More detailed comparisons between observation and theory are needed. Further observations, particularly with the Atacama Large Millimeter/Submillimeter Array, will take our gaze more deeply into circumstellar gas and dust clouds.

ALMA

The array allows observations of the surrounding dust and gas with unprecedented angular resolution and sensitivity. Astronomers are also planning to construct telescopes significantly larger than Subaru in the coming decades – including the Thirty Meter Telescope (TMT) and the European Extremely Large Telescope [E-ELT].

TMT

E-ELT

These should allow detailed studies of regions very close to newborn stars.

Note:

Astronomical Unit (AU) is a unit of distance. 1 AU corresponds to the average distance between the Earth and the Sun.

Paper and Research Team:

This research was supported by the Ministry of Science and Technology (MoST) of Taiwan (Grant Nos. 103-2112-M-001-029 and 104-2119-M-001-018). E.I.V. acknowledges the support from the Russian Ministry of Education and Science Grant 3.961.2014/K and RFBR grant 14-02-00719. R.D. was supported by Hubble Fellowship. M.M.D. acknowledges support from the Submillimeter Array through an SMA Postdoctoral Fellowship.
These observational results were published by Liu et al. as Circumstellar Disks of the Most Vigorously Accreting Young Stars in the Science Advances on February 5, 2016.

This research was conducted by:

Hauyu Baobab Liu (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan / European Southern Observatory, EU)
Michihiro Takami (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan)
Tomoyuki Kudo (Subaru Telescope, National Astronomical Observatory of Japan, USA)
Jun Hashimoto (National Astronomical Observatory of Japan, Japan)
Ruobing Dong (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan / Hubble Fellow / Department of Astronomy, UC Berkeley, USA)
Eduard I. Vorobyov (Department of Astrophysics, University of Vienna, Austria / Research Institute of Physics, Southern Federal University, Russia)
Tae-Soo Pyo (Subaru Telescope, National Astronomical Observatory of Japan, USA)
Misato Fukagawa (National Astronomical Observatory of Japan, Japan)
Motohide Tamura (National Astronomical Observatory of Japan, Japan / Department of Astronomy, Graduate School of Science, The University of Tokyo, Japan)
Thomas Henning (Max-Planck-Institut für Astronomie, Germany)
Michael M. Dunham (Harvard-Smithsonian Center for Astrophysics, USA)
Jennifer Karr (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan)
Nobuhiko Kusakabe (National Astronomical Observatory of Japan, Japan)
Toru Tsuribe (College of Science, Ibaraki University, Japan)

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

Subaru

ALMA

Solar Flare Telescope

Nobeyama Radio Observatory

Nobeyama Radio Observatory: Solar

Mizusawa VERA Observatory

Okayama Astrophysical Observatory

The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.