Orsay Survey of Atomic Hydrogen in the Galactic Plane
(displayed by Joachim Köppen Kiel Sept.2013/Jan.2019)

Some brief explanations

This tool shows the results of a survey of the Galactic Plane at the radio line of atomic hydrogen at 21 cm wavelength, done with the 3.3m diameter radio telescope in Orsay, south of Paris, near Orly airport, built and operated by J.J.Maintoux.

The data are in a datacube of galactic longitude (from 4° to 240° in steps of 2°), a single galactic latitude (0°), and radial velocity from -200 to +200 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 radial velocity, for a given value of the galactic latitude. The colour bar at the right hand side gives the relation between colour and the value varying linearly between minimum (violet) and maximum (red). This a map shows the spiral arms of the Milky Way, and indicates the galactic rotation curve: the white curve is the limit of the hydrogen emission for a constant rotation velocity of 230 km/s.
• the spectrum at the specified galactic longitude (and latitude=0°) 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. By assuming a constant rotation velocity, we can computing from the galactic longitude and the radial velocity of every pixel the true distance from the sun of this emission. 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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