Second Illkirch Survey of Galactic Hydrogen

Joachim Köppen Strasbourg Oct.2010/Jan.2018

Some brief explanations

This tool shows the results of the second survey at the radio line of atomic hydrogen at 21 cm wavelength, done with the ESA-Haystack radio telescope at the International Space University in Illkirch between July and September 2010.

The system temperature was about 1000 K or somewhat worse ...

The data were taken by staying for 10 min at each galactic longitude (from 0° to about 250° in steps of 2°) and in galactic latitude from -30° to +30° (in steps of 2°), with a coverage in radial velocity from -150 to +150 km/s. 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.


• 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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