Surveys of Galactic Hydrogen
Joachim Köppen Kiel Sept.2013 ... Jan.2019
Some brief explanations
This tool shows the results from several surveys of galactic hydrogen,
at the radio line of atomic hydrogen at 21 cm wavelength.
The data are in a datacube of galactic longitude (from -180° to +180°
or 0° to 360° in steps of 2° or 5°), galactic latitude
(from -30° to +30° in steps of 2°), and radial velocity
from -150 to +150 (or -400 to +400) km/s.
- The Illkirch Surveys were done with the
ESA-Haystack radio telescope (2.3m diameter, HBPW = 6.5°,
the 'old' SRT)
at the International Space University in Illkirch between 2010 and 2012.
The first (not shown) and second surveys were done with a system temperature above 1000 K,
the third with 700 K, and the fifth with about 300 K. The DataCube surveys with finer
resolution in galactic latitude were also done with 300 K. Integration times are 5 and
10 min at each position.
- GCO Surveys have been done since 2014 with the 2.3m radio telescope
(also the 'old' SRT)
at Grove Creek Observatory
west of Sydney. System temperature is about 170 K. Integration times are 5 and 10 min
at each position.
- A deep survey of the southern skies has been started in 2015 from GCO.
System temperature is about 170 K. 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.
- Furthermore, the area around the Magellanic Clouds has been mapped from GCO in 2014
with a system temperature of about 170 K and 10 min at each position. The test survey
in 2018 had Tsys = 500K and 2 hrs integration time.
- A Survey of the Galactic Plane was done in 2009 with the 3.3m diameter radio
telescope in Orsay, south of Paris, near Orly airport, built and operated
by J.J.Maintoux F1EHN.
- The DL0SHF Survey was done in 2013..2015 with the 9m antenna (HBPW = 1.9°)
at the DL0SHF Amateur Radio
and Ground Station in Rönne near Kiel. System temperature is about
100 K. The data were obtained by letting the sky drift across the antenna lobe
while recording continuously. Since at the time of observations the pointing
errors of the antenna had not yet been corrected, positions may differ by
about 1° from true values.
- For comparison, data from the professional LAB (= Leiden-Argentina-Bonn)
survey with 25m diameter dishes are shown, but smoothed to lower angular
resolutions, as one would observe with smaller radio telescopes.
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).
- 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.
Be aware that for the Magellanic Clouds Surveys this option is not sensible.
- 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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