|
Dawson et al. have presented the full data release for the Southern
Parkes Large-Area Survey in Hydroxyl (SPLASH) -- the most
sensitive large-scale survey of hydroxyl (OH) to-date. The survey of
the Southern Galactic Plane was undertaken in all four ground-state
transitions of the OH radical at 1612, 1665, 1667 and 1720 MHz with
the Parkes 64m radio-telescope, "Murriyang".
Great care needs to be taken in spectral line surveys in determining
the bandpass, a task which can be complicated by the presence of Radio
Frequency Interference (RFI). In the image above, the top panels show
waterfall plots of the 15 reference integrations in a single map file
in the 1612 MHz band, where each row of the image represents a single
spectrum with a 4s integration time. The colour scale runs from dark
(low) to light (high), with black (right-hand panel only) indicating
completely flagged channels. The white numbers and thin white dashed
lines indicate the groups of integrations comprising a single 4 second
reference position observation – 15 in total for a full 2 degree × 2
degree map file, each separated by about 4 minutes in time (for a
total 60s integration time on the reference position).
The horizonal axes show the channel number.
The bottom two panels show examples of the reference spectra as they would be applied to map data
(where the pink spectra are artifically offset for ease of viewing).
It can be seen that RFI has severely affected the 14th reference observation in this file,
rendering it unusable.
The preceding reference that
will replace it in processing is shown in its place in the right-hand plot.
The paper has been published in
Monthly Notices of the Royal Astronomical Society.
|
