Galactic images

The UK-led SPIRE instrument on board the Herschel Space Observatory has made its first astronomical observations, with spectacular results.

The first SPIRE images, together with first light observations from the other two Herschel instruments, were released last Friday by the European Space Agency (ESA).

The SPIRE camera responds to light at wavelengths between 250 and 500 microns. It is designed to look for emission from clouds of dust in regions where stars are forming in our own and other galaxies.

On 24 June, SPIRE was able to observe the sky for the first time. The telescope was trained on two galaxies to get a first impression of what the instrument could see. The images were taken before any attempt had been made to set up the instrument or to tune the image-processing software. The target galaxies showed up prominently and many other more distant galaxies were also seen in the field of view.

The images below show two galaxies, M66 and M74, at a wavelength of 250 microns. The images trace emission by dust in clouds where star formation is active and the nucleus and spiral arms show up clearly. Dust is part of the interstellar material that fuels star formation and the images effectively show the reservoirs of gas and dust that are ready to be turned into stars in the galaxies.

The frames are also filled with many other galaxies which are much more distant and only show up as point sources. There are also some extended structures, possibly because of clouds of dust in our own galaxy.

The images have given astronomers a foretaste of the scientific studies planned with SPIRE; the instrument will look at star formation close up in our own galaxy and in nearby galaxies and it will search for star-forming galaxies in the very distant universe.

Prof Matt Griffin of Cardiff University, who is the SPIRE principal investigator, said: ‘These quick first light observations have produced dramatic results when we consider that they were made on day one. Astronomers planning to use SPIRE are delighted because they can see straight away that the main scientific studies planned with the instrument are going to work extremely well. In fact, all three instruments on Herschel have now shown what they can do – and the results are spectacular.’

Prof Robert Kennicutt of the University of Cambridge, who will use Herschel to study nearby galaxies, added: ‘These first images from SPIRE reveal the cold dust and star formation in these galaxies in stunning detail and are a sneak preview of future observations that promise to revolutionise our understanding of star formation in the universe.’