Drift Scan Survey of Galactic Hydrogen with GCO SRT
Joachim Köppen Kiel Jul.2020-Dec.2020
Some brief explanations
This tool shows the results of of a drift scan survey of the Southern Hemisphere skies
in the radio line of atomic hydrogen at 21 cm wavelength, which covers as much of the
sky as possible with the 2.3m diameter
SRT at Grove Creek Observatory.
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 170 K. Please note that the
data cubes with 1 and 2° resolution are quite large and thus take some
time to load!
The 1° resolution cube is restricted to galactic latitudes between -50 and +50°,
while the 2° and 5° cubes cover all galactic latitudes.
Another survey was done in 2023, shown in resolutions 1 and 2°. From these data
the area around the Magellanic Clouds was extracted with resolutions 0.75, 0.5 and 0.3°.
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
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. 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.