SPLASH - The Southern Parkes Large-Area Survey in Hydroxyl


Welcome to the SPLASH homepage!

SPLASH is a survey of the Southern Milky Way with the Parkes radio telescope in all four ground-state transitions of the diatomic molecule hydroxyl (OH).

OH is found in cold, dusty clouds of interstellar gas known as molecular clouds. Molecular clouds are the "cradles of life", where stars, planets and complex molecules form. In order to answer the big questions of how stars and planets are born, we must understand the way in which molecular clouds condense from what is almost a vacuum, sparsely filled with atomic hydrogen, helium, and trace amounts of other elements.

OH is one of a handful of molecules that are found not only in the dense and dusty depths of molecular clouds, but also in their diffuse, partially atomic envelopes. In recent years, the ability of OH to trace this diffuse molecular gas has become very relevant, with the remarkable discovery that the "standard" spectral line tracers - the 21 cm radio emission from atomic hydrogen and 3 mm microwave emission from the CO molecule - fail to account for as much as half of the gas mass in the local interstellar medium. By observing interstellar OH molecules, at frequencies of 1612, 1665, 1667 and 1720 MHz, SPLASH is searching for hidden molecular gas in the Galaxy, and investigating whether OH may be used as signpost of regions where young molecular clouds are just beginning to form.

Bright maser emission from OH is also a valuable tool for probing a number of different astrophysical phenomena, including evolved stars, supernova remnants, and stellar nurseries deep within molecular clouds. As a blind survey for all four ground-state OH transitions, SPLASH is already cataloguing and studying hundreds of new maser sources throughout the Southern Sky.


The Parkes telescope (left) and early data from the SPLASH survey (right), showing emission and absorption from the OH 1612 MHz line in a small section of the Milky Way. More explanation on this figure can be found here

Last modified 7th June 2017.