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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".
The team identified numerous new examples of satellite line ‘flips’ – a
characteristic profile shape in which one line flips from emission to
absorption, and the other the reverse -– across closely-blended double
features. They confirm a preferred velocity orientation for these
profiles, with the a 1720- emission/1612-absorption component seen at
more negative velocities in the majority of cases.
This is consistent
with recent models explaining the flip as a signature of HII (ionized hydrogen)
region expansion. The figures above show
illustrative examples of satellite line ‘flips’,
The paper has been published in
Monthly Notices of the Royal Astronomical Society.
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