Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

HI4PI: A new all-sky survey of neutral hydrogen

20.10.2016

Two of the world's largest fully steerable radio telescopes, the 100-m dish at Effelsberg/Germany and the 64-m Parkes/Australia telescope, mapped the detailed structure of neutral hydrogen across the Northern and Southern hemispheres. Today, the complete survey, HI4PI, is released to the scientific community. It discloses a wealth of fine details of the large scale structure of the Milky Way's gas distribution. HI4PI is the product of a joined effort of astronomers of many countries and will be a mile stone for the decades to come.

Atomic hydrogen is the most abundant element in space. It is the prime constituent in almost all astronomical objects such as stars, galaxies, and even clusters of galaxies. Hydrogen consists of a single proton and is the simplest element in space. It was already formed during the big bang nucleosynthesis. If the proton is combined with an electron, it is called neutral atomic hydrogen, abbreviated as HI.


The entire sky in the light of neutral atomic hydrogen (HI) as seen by the Parkes and Effelsberg radio telescope with the Milky Way in the middle. .

HI4PI Collaboration


Two of the largest radio telescopes in the world, utilized for HI4PI, the high-resolution map of the full sky in the light of neutral hydrogen: Effelsberg (100-m, left) and Parkes (64-m, right).

Norbert Junkes (left image), Shaun Amy (right image).

In addition to the well-known hydrogen spectral lines at visual wavelengths, extremely faint hydrogen line emission can be observed at radio wavelengths, the so-called 21-cm line. Even though the emitted energy is tiny, the sheer amount of hydrogen in space makes the 21-cm line emission observable in nearly all galactic environments, even far beyond the stellar population of galaxies.

In 1951 three independent research groups from the United States, the Netherlands and Australia announced the first detection of HI 21-cm line emission. Now, 65 years later, an international collaboration of scientists from all over the world announced the release of a new full-sky 21-cm spectral line survey, called HI4PI.

HI4PI is an acronym for HI across the whole sky (the surface area of the full sphere corresponding to 4*PI steradian). The HI4PI collaboration, led by a German team from Bonn University and Max Planck Institute for Radio Astronomy (MPIfR), is publishing the results in the current issue of "Astronomy and Astrophysics".

With modern radio telescopes, HI is fairly easy to detect towards any direction on the sky. Mapping the whole sky is nevertheless time consuming and costly in terms of manual labor. To map the whole sky demanded more than a million individual observations with two of the World's largest radio telescopes, the 100-m telescope at Effelsberg, Germany, and the Parkes 64-m telescope in Australia. In total, dozens of Tera-bytes of raw data have been recorded. The raw data sets were processed by Astronomers in Bonn, yielding the final data product.

“Besides a careful calibration of the data, we also had to remove man-made noise from the data. This so-called radio frequency interference (RFI) is, for example, produced by telecommunication and broadcast stations, or military RADAR and pollutes the faint emission of the astronomical sources”, explains Benjamin Winkel from MPIfR, responsible for the data acquisition and processing in the HI4PI collaboration. “The computational effort for the data processing was huge, adding to the thousands of hours of observations thousands of hours of computing time.”

The new observations were only possible because the technical equipment at radio telescopes was hugely improved in the last decade. On the one hand, new receiving systems utilizing multi-pixel feeds increased the mapping speed by an order of magnitude. On the other hand, extremely capable spectrometers based on state-of-the-art digital processors became available. Previously, state-of-the-art HI data came from the Leiden-Argentine-Bonn survey (LAB), which is based on observations with 30-m class telescopes. The new HI4PI survey has twice the sensitivity and four times better angular resolution compared to the LAB survey.

Because HI is ubiquitous in the universe, HI4PI will serve as a major resource for researchers working with observational data at all wavelengths. As an example, X-ray and Gamma ray photons are partly absorbed, scattered or re-emitted at other wavelengths by Milky Way hydrogen during their journey from outer space to our telescopes. Therefore, the distribution of HI in the Milky Way significantly alters the incoming signal observed by high-energy telescopes. The HI4PI data set allows the scientists to correct for these disturbing effects, cleaning our window to the distant universe.

Also, for astrophysicists studying the Milky Way gas distribution itself, HI4PI will be a valuable new resource. Owing to the increased sensitivity and angular resolution much finer structures of the interstellar medium are now revealed. “Many studies that use pre-release data of the HI4PI survey have already been published in the last years, providing a wealth of new insights and amazing scientific results”, says Peter Kalberla from Bonn University, the leading senior scientist in the project.

“HI4PI sets a benchmark for the decades to come”, concludes Jürgen Kerp, also from Bonn University, the project coordinator and principal investigator of the Effelsberg survey. “Although upcoming new instruments such as the Square Kilometer Array (SKA) will push sensitivity and angular resolution to new realms, being radio interferometers they are by design insensitive to diffusely distributed HI gas. The HI4PI will be the prime resource to add this missing information to the SKA data.”

HI4PI data will be freely accessible on request from interested persons all over the world via CDS, the Strasbourg data center (after the embargo expires).


The team comprises the HI4PI Collaboration: N. Ben Bekhti, L. Flöer, R. Keller, J. Kerp, D. Lenz, and B. Winkel, moreover J. Bailin, M. R. Calabretta, L. Dedes, H. A. Ford, B. K. Gibson, U. Haud, S. Janowiecki, P. M.W. Kalberla, F. J. Lockman, N. M. McClure-Griffiths, T. Murphy, H. Nakanishi, D. J. Pisano, and L. Staveley-Smith.

Original Paper:

HI4PI collaboration: HI4PI: A full-sky HI survey based on EBHIS and GASS, 2016, Astronomy & Astrophysics, Online Publication October 20 (DOI: 10.1051/0004-6361/201629178).
URL: www.aanda.org/10.1051/0004-6361/201629178 (after the embargo expires)

Contact:

Priv.-Doz. Dr. Jürgen Kerp,
Argelander-Institut für Astronomie,
Universität Bonn.
Fon: +49 228 73-3667
E-mail: jkerp@astro.uni-bonn.de

Dr. Benjamin Winkel,
Radio-Observatorium Effelsberg,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49 2257 301-167
E-mail: bwinkel@mpifr-bonn.mpg.de

Dr. Norbert Junkes,
Press and Public Outreach
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49 228 525-399
E-mail: njunkes@mpifr-bonn.mpg.de

Weitere Informationen:

http://www.mpifr-bonn.mpg.de/pressreleases/2016/13

Norbert Junkes | Max-Planck-Institut für Radioastronomie

More articles from Physics and Astronomy:

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>