A Swinburne scientist is part of an international team of astronomers who have discovered over a dozen new galaxies halfway across the Universe. The discovery represents a major breakthrough in the field of distant galaxy ‘hunting’ and paves the way for more detailed studies of them.

The team was led by Nicolas Bouché from the Max Planck Institute for Extraterrestrial Physics in Germany and included Swinburne University of Technology astronomer Dr Michael Murphy.

Using the European Southern Observatory’s Very Large Telescope (VLT) in northern Chile, the astronomers used quasars to find the galaxies. Quasars are very distant objects of extreme brilliance, which are used as cosmic beacons to reveal galaxies lying between the quasar and Earth.

The galaxy’s presence is revealed by 'absorption lines' – dips in the spectrum of the quasar – caused by the absorption of light at a specific wavelength.

“We infer the galaxy's existence from the specific pattern of shadows they imprint onto the quasar's spectrum”, said Dr Murphy.

The team used huge catalogues of quasars, the so-called SDSS and 2QZ databases, to select quasars with dips. The next step was to search the patches of sky around these quasars for the foreground galaxies whose light comes from the time the Universe was only about 6 billion years old, less than half of its current age.

“The difficulty in actually spotting and seeing these galaxies stems from the fact that the glare of the quasar is too strong compared to the dim light of the galaxy,” said Bouché.

This is where observations taken with SINFONI on ESO’s VLT made the difference. SINFONI is an infrared 'integral field spectrometer' that simultaneously delivers very sharp images and highly resolved colour information (spectra) of an object on the sky.

Dr Murphy’s role was to find the dips in the spectrum of the quasars using a sophisticated search technique to pick out the absorption lines that reveal a galaxy is there.

“It’s the equivalent of finding needles in a haystack. For a long time we weren’t able to study the galaxies associated with the dips in quasar spectra because they were so distant and faint compared to the bright quasars. But now we can find the galaxies with SINFONI and try to understand the link between them and the absorption lines they cause.”

Dr Murphy said the work represents a big increase in how many distant galaxies have now been discovered in front of background quasars.

“One of the main things we’re trying to understand is what kind of galaxies we pick out using the absorption method. Contrary to what you would think, we have found some evidence that the stronger the absorption line is, the less massive the galaxy.“

“For a long time advancements in this field have been held up, but now we can start to understand more about how galaxies form and use that knowledge to understand galaxies at even larger distances from us.”

The research is presented in a paper in press in the Astrophysical Journal.