Surveys of Galactic Hydrogen
Joachim Köppen Kiel Sept.2013 ... Jul.2020

Some brief explanations

This tool shows the results from several surveys of galactic hydrogen, at the radio line of atomic hydrogen at 21 cm wavelength.

• The Illkirch Surveys were done with the ESA-Haystack radio telescope (2.3m diameter, HBPW = 6.5°, the 'old' SRT) at the International Space University in Illkirch between 2010 and 2012. The first (not shown) and second surveys were done with a system temperature above 1000 K, the third with 700 K, and the fifth with about 300 K. The DataCube surveys with finer resolution in galactic latitude were also done with 300 K. Integration times are 5 and 10 min at each position.


• GCO Surveys have been done since 2014 with the 2.3m radio telescope (also the 'old' SRT) at Grove Creek Observatory west of Sydney. System temperature is about 170 K. Integration times are 5 and 10 min at each position.
• A deep survey of the southern skies has been started in 2015 from GCO. System temperature is about 170 K. Each position was measured for 4 hours.
• The 'SouthPlane' surveys have been conducted since 2017 for testing after the system temperature had increased to 400 and 600 K. Integration times are 4 and 2 hours at each position. 'IllawongPlane' and 'SouthPlaneFour' cover only 0° latitude, with 600 K system temperature, and were reduced in a quick&rough way.
• In 2020 the entire accessible sky at GCO has been observed by daily drift scans. The data are stored in several data cubes with 1°, 2°, and 5° bins in longitude and latitude, and 2 km/s velocity bins from -200 to 400 km/s. The data cubes are available both without and with smoothing to adjacent position bins. The system temperature is near 170 K. Please note that the data cubes with 1 and 2° resolution are quite large and thus take some time to load!
• In 2023 another complete drift scan survey was done, shown in 1° and 2° bins. From these data the area around the Magellanic Clouds was extracted with resolutions 0.75, 0.5 and 0.3°. Yet another survey was taken from October 2023 to May 2024, by moving the telescope in 1° every day. The results are shown in resolutions of 1 and 2°.
• Furthermore, the area around the Magellanic Clouds has been mapped from GCO in 2014 and 2020 with a system temperature of about 170 K and 4 hours at each position.


• A Survey of the Galactic Plane was done in 2009 with the 3.3m diameter radio telescope in Orsay, south of Paris, near Orly airport, built and operated by J.J.Maintoux F1EHN.


• The DL0SHF Survey was done in 2013..2015 with the 9m antenna (HBPW = 1.9°) at the DL0SHF Amateur Radio and Ground Station in Rönne near Kiel. System temperature is about 100 K. The data were obtained by letting the sky drift across the antenna lobe while recording continuously. Since at the time of observations the pointing errors of the antenna had not yet been corrected, positions may differ by about 1° from true values.


• For comparison, data from the professional LAB (= Leiden-Argentina-Bonn) survey with 25m diameter dishes are shown, but smoothed to lower angular resolutions, as one would observe with smaller radio telescopes.

The results are shown as:

• one may chose the longitude range between 0°..360°, -90°..270°, -180°..180°, and -270°..90°


• false colour map of antenna temperature (i.e. the measured intensity) for galactic longitude and latitude, at a fixed value of the radial velocity. The colour bar at the right hand side gives the relation between colour and the value varying linearly between minimum (violet) and maximum (red).
• false colour map of antenna temperature for galactic longitude and radial velocity, for a given value of the galactic latitude. For glat=0° one obtains a map from which the spiral arms of the Milky Way become apparent and the galactic rotation curve, too (the white curve is the limit of the hydrogen emission for a constant rotation velocity of 230 km/s).
• false colour map of antenna temperature for radial velocity and galactic latitude, for a given value of the galactic longitude. From the map at glong=90° one can see that the outer spiral arms lie above the Galactic Plane, i.e. that the disc of the Milky Way is warped.
• the spectrum at the specified galactic longitude and latitude is a plot of antenna temperature as a function of radial velocity. The bump near v_rad = 0 km/s is the emission from neutral hydrogen clouds in the local spiral arm in which the Solar System is embedded. Other bumps are from other spiral arms.
• the deprojected view of the data for a fixed value of the galactic latitude shows how the Milky Way would look like when seen from the Northern Galactic Pole. Similarly, a view with fixed galactic longitude shows a cut through the disk, perpendicular to the Plane. By assuming a constant rotation velocity, we can computing from the galactic coordinates and the radial velocity of every pixel the true distance from the sun of the emitting parcel of gas. By simply associating the pixel's observed antenna temperature with this true position in the Galaxy the false colour map is generated.
  Be aware that for the Magellanic Clouds Surveys this option is not sensible.


• The values for the fixed parameter(s) can be changed by the user: enter a new value in the associated field and hit the return key. NOTE: if the display does not change, there's simply no data available for that position.
• Mouse position gives the values of all coordinates of the current position of the mouse.

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