Observations of Galactic Hydrogen with GCO SRT
Joachim Köppen Kiel Jan.2018 ... Nov.2020
Some brief explanations
This tool shows the results of surveys of the Southern Hemisphere skies in the
radio line of atomic hydrogen at 21 cm wavelength, done with the 2.3m diameter
SRT at Grove Creek Observatory.
The system temperature is about 170 K.
The first surveys were done by pointing to individual positions, with
integration times of 5 or 10 min per position.
Also shown are the data from GCO combined with the surveys of the northern
sky, done with ESA-Haystack radio telescope of
the same type, at Illkirch in France.
A deep survey of the southern skies was started in 2015 from GCO.
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 again near 170 K. Please note that the
data cubes with 1 and 2° resolution are quite large and thus take some
time to load!
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.