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.
- 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
vrad = 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
- 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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