MPIfR: HI4PI: A New All-Sky Survey of Neutral Hydrogen

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MPIfR: HI4PI: A New All-Sky Survey of Neutral Hydrogen

Post by bystander » Thu Oct 20, 2016 10:24 pm

HI4PI: A New All-Sky Survey of Neutral Hydrogen
Max Planck Institute for Radio Astronomy |2016 Oct 19
[img3="The entire sky in the light of neutral atomic hydrogen (HI) as seen by the Parkes and Effelsberg radio telescope. Our host galaxy, the Milky Way, appears as a luminous band across the sky with the Galactic Center in the middle. The Magellanic Clouds (Large and Small Magellanic Cloud) are prominently visible in orange colors below the Galactic plane. They are surrounded by huge amounts of gas, which was forcefully disrupted from their hosts by gravitational interaction. The HI emission of the Andromeda galaxy (M31) and its neighbor, Triangulum (M33), is also easy to spot as bright purple ellipses in the South-western part of the map. The gas motion is color coded with different hue values, and the visual brightness in the image denotes the intensity of the received HI radiation. (© HI4PI Collaboration)"] ... 704853.jpg[/img3][hr][/hr]
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. ...

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. ...

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HI4PI: A full-sky HI survey based on EBHIS and GASS - HI4PI Collaboration
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