China Science & Technology Forum

[Keel]

EAST Achieves 100s World Record Steady-state High Performance Plasma
2017-07-05

EAST superconducting tokamak made an exciting advance in achieving a stable 101.2 second steady-state high confinement plasma, creating a new world record in long-pulse H-mode operation on July 3rd night.

The obtained high confinement mode features the edge localized modes (ELMs) with small perturbation amplitude under the condition of low-momentum injection with pure RF (LHCD, ICRF, ECRH) wave heating, actively cooled ITER-like monoblock tungsten divertor. With effective control of the divertor target heat load and tungsten impurity influx and the center chord average electron density being maintained at > 50% Greenwald density limit, EAST achieved a fully non-inductive current driven steady-state high-performance plasma with a confinement enhancement factor H98y2 greater than 1.1 for more than 100 seconds. All the plasma parameters, including recycling, particle and heat fluxes, reached truly steady-state after 20s, the wall saturate time for the W divertor and maintained stable to the end of discharge.

Excited about the results, Chief Operator Xianzu Gong immediately shared the good news with some of EAST domestic and international partners in midnight via social media. Having operating EAST since 2006, Gong has witnessed every advance made on the machine as well as its setbacks. This breakthrough, he believes, indicates EAST will “continue to play a key role on both physics and engineering fronts of steady-state operation, and has significant scientific implications for the International Thermonuclear Fusion Reactor (ITER) and the future China Fusion Engineering Test Reactor (CFETR)”.

“It is a success of joint efforts,” added Gong. The EAST team has worked together with their collaborators at home and abroad over the past decade solving a series of key technical and physical issues closely related to the steady-state operation, and carried out in-depth scientific research on integrated operation scenarios with effective coupling of multi-scale physical processes.

EAST 2017 experimental campaign will go on for about one more month and the second round of experiment will start in autumn of this year.

Basic parameters of the world’s longest 101.2 s high confinement discharge achieved on EAST （Bt=2.5T, PRF=3.0MW, ne/neGW=0.55, Te=4.0KeV, H98y2=1.1, Upper single null configuration ）


EAST Achieves 100s World Record Steady-state High Performance Plasma----Institute of Plasma Physics Chinese Academy Of Scieneces

Congrats! Still a long long way to go!

 

[JSCh]

Using buoys, China builds tsunami monitoring network in South China Sea
(People's Daily Online) 17:06, July 05, 2017

Technicians deploy a tsunami detection buoy into the water. (file photo)

The Manila Trench is associated with frequent earthquakes in the Pacific Ocean. Because of this, China has deployed two sets of tsunami detection buoys along the Trench for the first time, marking the completion of the country's tsunami monitoring buoys network in South China Sea, Science and Technology Daily reported on July 5.

The buoys are equipped with new technology, which has significantly improved their accuracy. They can detect as little as 5 millimeters in sea level rise caused by tsunamis. Once there is a tsunami earthquake, the subtle fluctuations are detected and that data is sent via satellites to the South China Sea branch of the China's State Oceanic Administration and the National Tsunami Early Warning Center.

The detection network is expected to provide a two-hour early warning for residents in China's coastal areas and countries in the South China Sea.

The two sets of tsunami detection buoys is an important component of China's tsunami monitoring and early warning system.

 

[JSCh]

06 July 2017
Chances of hypersonic travel heat up with new materials discovery

​

Researchers at The University of Manchester in collaboration with Central South University (CSU), China, have created a new kind of ceramic coating that could revolutionise hypersonic travel for air, space and defense purposes.

Hypersonic travel means moving at Mach five or above, which is at least five times faster than the speed of sound. When moving at such velocity the heat generated by air and gas in the atmosphere is extremely hot and can have a serious impact on an aircraft or projectile’s structural integrity. That is because he temperatures hitting the aircraft can reach anywhere from 2,000 to 3,000 °C.

The structural problems are primarily caused by processes called oxidation and ablation. This is the when extremely hot air and gas remove surface layers from the metallic materials of the aircraft or object travelling at such high speeds. To combat the problem materials called ultra-high temperature ceramics (UHTCs) are needed in aero-engines and hypersonic vehicles such as rockets, re-entry spacecraft and defence projectiles.

But, at present, even conventional UHTCs can’t currently satisfy the associated ablation requirements of travelling at such extreme speeds and temperatures. However, the researchers at The University of Manchester’s and the Royce Institute, in collaboration with the Central South University of China, have designed and fabricated a new carbide coating that is vastly superior in resisting temperatures up to 3,000 °C, when compared to existing UHTCs.

Professor Philip Withers, Regius Professor from The University of Manchester, says: “Future hypersonic aerospace vehicles offer the potential of a step jump in transit speeds. A hypersonic plane could fly from London to New York in just two hours and would revolutionise both commercial and commuter travel.

“But at present one of the biggest challenges is how to protect critical components such as leading edges, combustors and nose tips so that they survive the severe oxidation and extreme scouring of heat fluxes at such temperatures cause to excess during flight.”

Future hypersonic aerospace vehicles offer the potential of a step jump in transit speeds. A hypersonic plane could fly from London to New York in just two hours and would revolutionise both commercial and commuter travel.
Professor Philip Withers​

So far, the carbide coating developed by teams in both University of Manchester and Central South University is proving to be 12 times better than the conventional UHTC, Zirconium carbide (ZrC). ZrC is an extremely hard refractory ceramic material commercially used in tool bits for cutting tools.

The much improved performance of the coating is due to its unique structural make-up and features manufactured at the Powder Metallurgy Institute, Central South University and studied in University of Manchester, School of Materials. This includes extremely good heat resistance and massively improved oxidation resistance.

What makes this coating unique is it has been made using a process called reactive melt infiltration (RMI), which dramatically reduces the time needed to make such materials, and has been in reinforced with carbon–carbon composite (C/C composite). This makes it not only strong but extremely resistant to the usual surface degradation.

Professor Ping Xiao, Professor of Materials Science, who led the study in University of Manchester explains: “Current candidate UHTCs for use in extreme environments are limited and it is worthwhile exploring the potential of new single-phase ceramics in terms of reduced evaporation and better oxidation resistance. In addition, it has been shown that introducing such ceramics into carbon fibre- reinforced carbon matrix composites may be an effective way of improving thermal-shock resistance.”

Advanced Materials

Advanced materials is one of The University of Manchester’s research beacons - examples of pioneering discoveries, interdisciplinary collaboration and cross-sector partnerships that are tackling some of the biggest questions facing the planet.

Referecne: "Ablation-resistant carbide Zr0.8Ti0.2C0.74B0.26 for oxidizing environments up to 3,000 °C" Yi Zeng, Dini Wang, Xiang Xiong, Xun Zhang, Philip J. Withers, Wei Sun, Matthew Smith, Mingwen Bai & Ping Xiao Article number: 15836 (2017) doi:10.1038/ncomms15836


http://www.manchester.ac.uk/discove...-travel-heat-up-with-new-materials-discovery/

Abstract

Ultra-high temperature ceramics are desirable for applications in the hypersonic vehicle, rockets, re-entry spacecraft and defence sectors, but few materials can currently satisfy the associated high temperature ablation requirements. Here we design and fabricate a carbide (Zr0.8Ti0.2C0.74B0.26) coating by reactive melt infiltration and pack cementation onto a C/C composite. It displays superior ablation resistance at temperatures from 2,000–3,000 °C, compared to existing ultra-high temperature ceramics (for example, a rate of material loss over 12 times better than conventional zirconium carbide at 2,500 °C). The carbide is a substitutional solid solution of Zr–Ti containing carbon vacancies that are randomly occupied by boron atoms. The sealing ability of the ceramic’s oxides, slow oxygen diffusion and a dense and gradient distribution of ceramic result in much slower loss of protective oxide layers formed during ablation than other ceramic systems, leading to the superior ablation resistance.​

 

[JSCh]

Effective component in ginseng successfully cultivated
By Cai Wenjun | 14:54 UTC+8 July 4, 2017 |

Online Edition

LOCAL scientists said they are able to cultivate ginsenoside, an effective component in ginseng from yeast. This means the component can be produced in a professional workshop instead of growing on the land, free of threat from water and soil pollution and pesticide residue.

It is one of the new achievements of synthetic biology, which has attracted scientists all over the world, experts said during a forum on the subject launched in Shanghai.

“Synthetic biology is an interdisciplinary branch of biology and engineering. It has become a very popular topic in the science field,” said Wang Yong from the Institute of Plant Physiology and Ecology and vice director of synthetic biology key laboratory of the Chinese Academy of Sciences. “Our scientists have been able to cultivate special plants through the technology, thus reducing plant’s disease and boosting their production.”

According to Wang, the new technology can be very meaningful to traditional Chinese medicine, grain, new material development.

“Scientists have started to use bacteria to develop a protein the same with cobweb for clothing materials,” he said. “Local scientists also developed an intelligent diabetes management system with combination of biology and electric engineering.”

 

[JSCh]

China’s quantum satellite adds two new tricks to its repertoire
Era of ultrasecure communication inches closer

11:00am, July 7, 2017
By Emily Conover

BEAM ME UP, SCOTTY China’s quantum satellite has met two more milestones, performing quantum teleportation and transmitting quantum encryption keys through space. Scientists teleported the properties of photons, or particles of light, from a ground station in Tibet (shown in this composite photo) to the satellite.

Xinhua/Alamy​

A record-breaking quantum satellite has again blown away the competition, achieving two new milestones in long-distance quantum communications through space.

In June, Chinese researchers demonstrated that the satellite Micius could send entangled quantum particles to far-flung locations on Earth, their properties remaining intertwined despite being separated by more than 1,200 kilometers (SN Online: 6/15/17). Now researchers have used the satellite to teleport particles’ properties and transmit quantum encryption keys. The result, reported in two papers published online July 3 and July 4 at arXiv.org, marks the first time the two techniques have been demonstrated in space.

In quantum teleportation, the properties of one particle are transferred to another. The scientists first sent particles of light, or photons, from the ground to the satellite — a distance of up to 1,400 kilometers. When the researchers made particular measurements of other photons on the ground, the spacefaring particles took on the properties of the landlubbers, thanks to quantum entanglement between the earthbound and satellite-based particles. Although it’s a far cry from the Star Trek variety of teleportation, the process is an important ingredient of quantum communication.

Quantum key distribution is a method of creating a secret string of random numbers that can be used to encrypt communications. The researchers beamed photons from the satellite to Earth over distances of up to 1,200 kilometers, using the photons’ polarization, the orientation of their electromagnetic waves, to transmit a string of random numbers with utmost security.

Quantum communication via satellite can reach greater distances than land-based transmission, because in space, particles don’t get absorbed by the atmosphere. The new results pave the way for a global quantum internet that would provide for ultrasecure communications and allow quantum computers to work together.

Citations
J.-G. Ren et al. Ground-to-satellite quantum teleportation. arXiv:1707.00934. Posted July 4, 2017.

S.-K. Liao et al. Satellite-to-ground quantum key distribution. arXiv:1707.00542. Posted July 3, 2017.

​

China’s quantum satellite adds two new tricks to its repertoire | Science News

 

[JSCh]

Public Release: 7-Jul-2017
Strange silk: Why rappelling spiders don't spin out of control
Dragline silk from golden orb weaver spiders dissipates energy to prevent spinning

American Institute of Physics

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The golden silk orb weaver (Nephila pilipes) creates dragline silk that prevents it from spinning while hanging from its web.
Credit: Kai Peng of Huazhong University of Science and Technology

WASHINGTON, D.C., July 7, 2017 -- The last time you watched a spider drop from the ceiling on a line of silk, it likely descended gracefully on its dragline instead of spiraling uncontrollably, because spider silk has an unusual ability to resist twisting forces.

In a new paper appearing this week in Applied Physics Letters, from AIP Publishing, researchers from China and the U.K. showed that unlike human hair, metal wires or synthetic fibers, spider silk partially yields when twisted. This property quickly dissipates the energy that would otherwise send an excited spider spinning on the end of its silk.

"Spider silk is very different from other, more conventional materials," said Dabiao Liu of Huazhong University of Science and Technology. "We find that the dragline from the web hardly twists, so we want to know why."

A greater understanding of how spider silk resists spinning could lead to biomimetic fibers that mimic these properties for multiple potential uses such as in violin strings, helicopter rescue ladders and parachute cords. "If we understood how spider silk achieves this, then maybe we could incorporate the properties into our own synthetic ropes," said David Dunstan of Queen Mary University of London.


---> Strange silk: Why rappelling spiders don't spin out of control | EurekAlert! Science News

###​

The article, "Peculiar torsion dynamical response of spider dragline silk," is authored by Dabiao Liu, Longteng Yu, Yuming He, Kai Peng, Jie Liu, Juan Guan and D. J. Dunstan. The article appeared in Applied Physics Letters July 5, 2017 (DOI: 10.1063/1.4990676) and can be accessed at http://aip.scitation.org/doi/full/10.1063/1.4990676.

 

[JSCh]

Chinese city completes tests of quantum communication network
Source: Xinhua| 2017-07-10 00:16:47|Editor: Mu Xuequan



JINAN, July 9 (Xinhua) -- Quantum communication network, which boasts ultra-safe connection impenetrable to hackers, is expected to be put into commercial use in a Chinese city by the end of next month.

Jinan Institute of Quantum Technology announced Sunday that the network, connecting Communist Party and government bodies in Jinan, capital of east China's Shandong Province, had lately been tested and the designers were satisfied with its performance, especially in secured communications.

Liu Hong, a professor with Shandong University who was involved in the test, said the network has proved to be in a "very ideal" condition.

In the test, which involved over 50 programs, the network transmitted data with quantum encryption keys among nearly 200 terminals in the city. Between users, more than 4,000 keys were generated in just a second, said Zhou Fei, an assistant director of the institute.

Quantum communication uses quantum entanglement of photons to make sure that nobody taps into the line, for doing so would inevitably corrupt the signal.

In quantum communication, any interference is detectable. Two parties can exchange secret messages by sharing an encryption key encoded in the properties of entangled particles.

Zhou said the success of the test is a landmark in the development of quantum communication technology worldwide, paving the way for its commercial use first in government and then in finance, energy and other sectors.

 

[JSCh]

China's first unmanned lifeguard speedboat unveiled in Hefei
By Wang Xueying
2017-07-10 11:25 GMT+8

In China, lifeguards might soon join a growing list of professionals who will be replaced by robots or at least working with them in their jobs. The Institute of Intelligent Machines (IIM) under the Chinese Academy of Sciences announced recently that it has launched the country's first unmanned speedboat designed to save people from drowning.

The craft made its debut in Hefei, capital of east China's Anhui Province, to monitor swimmers and tourists at the Swan Lake, where drownings often occur, said the IIM.

The speedboat is equipped with cameras, GPS and infrared sensors to detect "moving targets" in the water, said Yu Yangdao, who led the unmanned craft's development.

Once a swimmer crosses the danger line, the speedboat will locate him or her, calculate the risk of drowning, and send a signal to the command center. The rescue team will then be alerted to take actions at once for the swimmer in danger.

A model of the China-developed unmanned survey vessel on display. /VCG Photo

In fact, the use of driverless vessels in China has been restricted due to environmental factors for a long time. Yu said the unmanned lifeguard speedboat marked a breakthrough in China, whose unmanned vessels have been technologically inferior to the ones manufactured in the United Stated and Israel in the past.

In the future, the unmanned speedboat will be used to patrol rivers, reservoirs, lakes, and seas.

 

[JSCh]

China unlocks key technologies for wave power
By Shan Xin (People's Daily Online) 13:53, July 11, 2017

A wave energy device developed by No. 38 Research Institute of CETC (CETC38) passed state acceptance criteria on July 10.

The institute has made important progress in key technologies, such as hydraulic conversion and control, as well as power inversion. Constant output can now be realized and power can be stored, even in a wave of less than 0.5 meters in height.

The institute has been testing the technology for three years. Smart integrated control and wide-range inverter technologies are used to improve the efficiency of power conversion. The results proved to be successful, as the device can float and absorb waves, thus storing and generating power.

The head of the project, Wang Zhen, introduced the highlights of the device: “The floater rides waves like a ship and can return to the shore if a major storm appears. Installed capacity of the device is 5 kilowatts, but more can be installed in the future. Standard electricity can be provided through a grid connection.”

 

[JSCh]

CSNS RCS Proton Beam Accelerated to 1.6 GeV
Jul 11, 2017

On July 7, 2017, scientists and technicians from the China Spallation Neutron Source (CSNS) successfully accelerated a proton beam to 1.6 GeV in the Rapid Cycling Synchrotron (RCS), marking a key step in beam commissioning as well as an important milestone for the CSNS project.

The first round of RCS beam commissioning began on May 31, 2017, and ended with a successful beam accumulation and extraction to the R-Dump on June 5, 2017. The second round began on July 3, 2017, and the proton beam was accelerated to 1.6 GeV on July 7, 2017. Two days later, the beam transmission rate became very close to 100%, with barely any beam loss through the whole process.

The RCS at CSNS is the first rapid cycling synchrotron in China. There were many theoretical and technical challenges in the design, construction and beam commissioning, one of which was to complete injection, accumulation, acceleration and extraction of a proton beam within 20 ms. After much sustained effort, the CSNS team has successfully overcome these difficulties.

"We have worked on improving the accelerator technology for CSNS for many years. It is our joint effort that has made it successful,” said Professor WANG Sheng, deputy director of the Accelerator Division of CSNS.


CSNS RCS Proton Beam Accelerated to 1.6 GeV---Chinese Academy of Sciences

 

[ashok321]

• BMW opens R&D in China, largest outside Germany

BEIJING: BMW motors on Thursday opened a new research and development (R&D) centre in China, the largest outside of Germany.

The new R&D centre, covering an area of over 40,000 sq.metres, is located in Shenyang, capital of Liaoning province, reports Xinhua news agency.

It is an extension of the original one built in 2012, and is five times larger than the first-stage project.

About 75 per cent of the 800-plus research personnel are Chinese, the company said, adding that the centre will focus on new energy technology to establish a complete R&D and production chain in China.


China has become the largest single market for BMW automotive vehicles. Earlier in May, the BMW assembly plant in Shenyang's Dadong district began operations.

Last January, an engine plant also began production in Shenyang.

 

[cirr]

Chinese scientists crack secret of 'winner effect'

2017-07-14 09:23

Xinhua Editor: Gu Liping

Chinese researchers may have revealed the secret of why animals increase their probability of victory after previous winnings, a phenomenon known as the "winner effect."

In a study published Thursday in the U.S. journal, Professor Hailan Hu's research group from Zhejiang University in China reported identifying for the first time a neural circuit in the brains of mice that plays a role in social dominance.

Stimulating brain cells in this circuit, known as dorsalmedial prefrontal cortex (dmPFC), significantly boosted a mouse's chance of becoming the "winner" during aggressive encounters with other mice.

"Getting to the top of social hierarchy is often not a matter of body size or brute strength, but rather determined by intrinsic mental factors such as grit, as well as extrinsic factors such as history of winning. For example, social dominance can be reinforced by a phenomenon known as the 'winner effect,'" Hu said. "However, the neural mechanism that mediates these intrinsic and extrinsic factors was poorly understood."

For the study, Hu's team performed a standard social dominance test that put male mice in a tube to face each other. Usually the subordinate animal would retreat and back out of the tube.

Then, the researchers recorded how much each one engages in certain behaviors such as push initiation, push-back, resistance, retreat, or stillness.

By monitoring individual brain cells in the dmPFC during such tests, they found a particular subset became more active during both push and resistance behaviors.

In mice with an established social rank, the researchers inhibited this subset of dominance brain cells using a drug and found within hours, these mice engaged in significantly fewer and shorter pushes and push-backs, but in more retreats.

Next the researchers used optogenetics to stimulate the dmPFC cells continuously during a social dominance encounter.

This instantaneously induced winning against previously dominant opponents with a 90 percent success rate, without affecting the motor performance or anxiety level.

"Importantly, dmPFC activation does not seem to boost dominance by enhancing basal aggression level or physical strength, but rather by initiating and maintaining more effortful behaviors during social competition," Hu said.

The findings could have important implications for treating psychiatric diseases, the researchers said.

"Considering that an excess or lack of dominance drive is associated with many personality disorders and mental problems, our results might shed light on the treatment of these psychiatric diseases," the study said.

http://www.ecns.cn/2017/07-14/265363.shtml

 

[cirr]

China’s third science center to take shape by 2020

By Zhang Huan (People's Daily Online)

July 13, 2017

The science center in Zhangjiang, Shanghai (file photo)

China’s third comprehensive national science center in Huairou, Beijing, is to take shape by 2020 and become world-renowned by 2030. The projections are based on the construction plan and outlook of the center as disclosed at the first international seminar on comprehensive science centers held on July 12, Xinhuanet.com reported.

The science center will focus on key scientific areas, including physical science, space science and geosciences, in order to give full support to innovation of core technologies in relation to development of national economy and emerging industries.

Meanwhile, construction of the centre’s first five interdisciplinary platforms is underway according to plans.

Approved by China’s National Development and Reform Commission as well as the Ministry of Science and Technology in May, the center is China’s third after those in Zhangjiang, Shanghai and Hefei, Anhui province.

http://en.people.cn/n3/2017/0713/c90000-9241399.html

 

[JSCh]

Brain activity helps build an alpha male
Experiments with dueling mice locate a brain region that helps them jump the pecking order

• By Laurel Hamers
• 2:00pm, July 13, 2017

Boosting the activity of certain brain cells can help a mouse climb the social ladder.

Nerve cells in a region called the dorsomedial prefrontal cortex appear to control whether male mice are dominant or submissive to other males, researchers report in the July 14 Science. The finding adds to previous evidence that this brain region is involved in social interactions in mammals.

Like men flexing muscles or flaunting sports cars to win status, male mice compete to establish a social pecking order. When every mouse knows his place, there can be less social conflict in the long run, says James Curley, a neurobiologist at the University of Texas at Austin who wasn’t part of the study.

In dominance tests, researchers pitted mice head-to-head in a plastic tube too narrow for the animals to pass each other. With no way forward, the lower-ranking mouse eventually retreats, pushed out of the tube by the more dominant mouse.

Researchers recorded the activity of individual nerve cells, or neurons, in mice’s brains while they engaged in the tube test. A group of neurons in the dorsomedial prefrontal cortex fired faster when mice were pushing forward to claim space in the tube, and fired more slowly as the mice retreated, says study coauthor Hailan Hu, a neuroscientist at Zhejiang University in Hangzhou, China.

Hu’s team then manipulated the activity of those neurons and once again measured the mice’s performance in the tube. Mice with these neurons inactivated via druglike small molecules didn’t try as hard on the tube task and were more likely to lose the competition, the researchers found. Mice with those neurons amped up with light, on the other hand, won against opponents who had previously beaten them. If those mice won enough times in one day, they’d even keep their newly elevated status for two or three days.

Story continues below video

ALPHA MOUSE Researchers put male mice head-to-head in a tube and observed their behavior to determine dominance. The bars along the top of the screen tracks each mouse’s behavior moment by moment — whether he’s pushing, resisting or retreating. Eventually, the dominant mouse pushes the subordinate one out of the tube. T. Zhou et al/Science 2017

Other studies have also suggested a role for the prefrontal cortex in controlling social dynamics in several species, including humans, Curley says. The new study adds detail by allowing the researchers to track how neural firing influences behavior immediately and then follow the effect over time.

However, the tube experiment measures dominance dynamics in pairs of mice, Curley points out, rather than in larger groups. “Whether the same mechanism underlies social dominance under all contexts is yet to be discovered,” he says.

Other factors, such as an animal’s size, can also influence its ability to win a fight. But Hu says that persistence is key, and that this group of neurons appears to affect that quality. “In risk tests, what's important is how much effort you want to put into the competition,” she says. “Some mice quit easily.”

Mouse studies like this one don’t translate directly to humans. But they allow scientists to study the neurobiology of dominance behaviors in levels of detail that aren’t possible in human subjects.

The study tested only male mice. In the future, Hu wants to find out whether a similar brain mechanism holds for female mice, too.

Citations

T. Zhou et al. History of winning remodels thalamo-PFC circuit to reinforce social dominance. Science. Vol. 357, July 14, 2017, p. 162. doi: 10.1126/science.aak9726.
​

Brain activity helps build an alpha male | Science News

 

[JSCh]

FOR IMMEDIATE RELEASE: July 11, 2017
RELEASE NO: NOAO 17-03
Distant Galaxies ‘Lift the Veil’ on the End of the Cosmic Dark Ages

Astronomers studying the distant Universe have found that small star-forming galaxies were abundant when the Universe was only 800 million years old, a few percent of its present age. The results suggest that the earliest galaxies, which illuminated and ionized the Universe, formed at even earlier times.

Long ago, about 300,000 years after the beginning of the Universe (the Big Bang), the Universe was dark. There were as yet no stars and galaxies, and the Universe was filled with neutral hydrogen gas. At some point the first galaxies appeared, and their energetic radiation ionized their surroundings, the intergalactic gas, illuminating and transforming the Universe.

While this dramatic transformation is known to have occurred sometime in the interval between 300 million years and 1 billion years after the Big Bang, determining when the first galaxies formed is a challenge. The intergalactic gas, which is initially neutral, strongly absorbs and scatters the ultraviolet light emitted by the galaxies, making them difficult to detect.

To home in on when the transformation occurred, astronomers take an indirect approach. Using the demographics of small star-forming galaxies to determine when the intergalactic gas became ionized, they can infer when the ionizing sources, the first galaxies, formed. If star forming galaxies, which glow in the light of the hydrogen Lyman alpha line, are surrounded by neutral hydrogen gas, the Lyman alpha photons are readily scattered, much like headlights in fog, obscuring the galaxies. When the gas is ionized, the fog lifts, and the galaxies are easier to detect.

A new study taking this approach has discovered 23 candidate Lyman alpha emitting galaxies (LAEs) that were present 800 million years after the Big Bang (at a redshift of z~7), the largest sample detected to date at that epoch. The study, “Lyman-Alpha Galaxies in the Epoch of Reionization” (LAGER), was carried out by an international team of astronomers from China, the US, and Chile using the Dark Energy Camera (DECam) on the CTIO 4-m Blanco telescope.

While the study detected many LAEs, it also found that LAEs were 4 times less common at 800 million years than they were a short time later, at 1 billion years (at a redshift of z~5.7). The results imply that the process of ionizing the Universe began early and was still incomplete at 800 million years, with the intergalactic gas about half neutral and half ionized at that epoch. The low incidence rate of LAEs at 800 million years results from the suppression of their Lyman alpha emission by neutral intergalactic gas.

The study shows that “the fog was already lifting when the universe was 5% of its current age”, explained Sangeeta Malhotra (Goddard Space Flight Center and Arizona State University), one of the co-leads of the survey.

Junxian Wang (USTC), the organizer of the study, further explained, “Our finding that the intergalactic gas is 50% ionized at z ~ 7 implies that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang.”

For Zhenya Zheng (Shanghai Astronomical Observatory, CAS), the lead author of the paper describing these results, “800 million years is the current frontier in reionization studies.” While hundreds of LAEs have been found at later epochs, only about two dozen candidate LAEs were known at 800 million years prior to the current study. The new results dramatically increase the number of LAEs known at this epoch.

“None of this science would have been possible without the widefield capabilities of DECam and its community pipeline for data reduction,” remarked coauthor James Rhoads. “These capabilities enable efficient surveys and thereby the discovery of faint galaxies as well as rare, bright ones.”

To build on these results, the team is “continuing the search for distant star forming galaxies over a larger volume of the Universe”, said Leopoldo Infante (Pontificia Catolica University of Chile and the Carnegie Institution for Science), “to study the clustering of LAEs.” Clustering provides unique insights into how the fog lifts. The team is also investigating the nature of these distant galaxies.

Reference:
“First Results from the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Cosmological Reionization at z ~ 7,” Zhenya Zheng et al. 2017, Astrophysical Journal Letters, 842, 22.
Preprint: https://arxiv.org/abs/1703.02985​

Cerro Tololo Inter-American Observatory is managed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.


National Optical Astronomy Observatory Press Release: Distant Galaxies ‘Lift the Veil’ on the End of the Cosmic Dark Ages